Lock the bathroom
Submit letters of resignation for other employees
Krazy-glue someone’s pens and pencils into their pencil cup.
Replace the paper towels with toilet paper. Its good for wiping up but doesnt dry for crap (HA!).
To mess with the boss/mailroom, have cubicle musical chairs. When they aren’t looking have everyone with a light workload change cubicles and wait for them to come looking.
Red food dye in the watercooler. Any color for that matter.
Have everyone park thier cars in the parking lot to spell something or make an image.
I’ll think of more. I enjoy a good mindfuck but I won’t get an office job till I get my degree.
Take all the paper clips in someone’s drawer or in a paper clip holder and link them all together. Then lower the chain into the container/drawer so that they look like a pile again. If you’re lucky, you’ll be there when they go to try and take one. 
Forthwith: My catalogue of overly-technical jokes:
One: Voices from the grave
The previous place I worked at was the kind of place where they played music during the day. A few of us technical lads eventually augmented the aging stereo system with an MP3 jukebox that people could work over the company intranet. All was well and good.
One evening, while at home, I noticed via MSN Messnger that one of my colleagues was still at the office. I should mention that the office was an old building, reputed to have been a plague hospital, next to a graveyard and with tall trees that tap at the windows when there’s a breeze. Most of the female staff refused to stay past sunset.
With devious intent, I recorded myself speaking my colleague’s name in an eerie tone of voice and applied a quick echo filter and a weird flange effect. Then I used VPN to connect to the work network and uploaded the WAV file onto the jukebox server. A little wrangling with Terminal Services and I was able to play this wav file, very quietly, over the office stereo using WinAmp.
I played it over and over at irregular intervals, changing the volume, but still keeping it pretty quiet. I also uploaded a couple of variations on the same theme, each with odd audio effects applied with CoolEdit. I kept it up until I saw him sign out of Messenger.
The next morning I learned that he’d fled the building in terror and was claiming that ghosts were speaking to him. Eventually I had to let him in on the gag of course. Luckily I chose to break the news when there were plenty of people around to pull him off me.
Two: Remote Control
Earlier in my career, when I first discovered the magic of DCOM, I decided that the best use for this technology was evil. I wrote a program that would allow me, by remote control, to simulate monitor problems and open/close the CD tray door on another computer.
I installed the nefarious components on our network engineer’s PC and, for the next week, randomly made the picture on his monitor jiggle, wave, scroll and flicker. I also opened his CD tray door every time he put his coffee down in front of it.
He was the kind of guy who could work up a good apopleptic rage over the malfunction of small devices. I almost felt sorry for his monitor as it received its regular beatings during that week.
Three : Mysterious Crashes
An important part of the network at a law firm I used to work for was a big Unix server running Informix that stored all of the billing data. Assigned to look after this monster was one of the most annoying men ever to walk the face of the Earth. I won’t bore you with a list of his social atrocities; suffice to say he was not well liked.
I wrote a piece of software that would function like a telnet proxy server and, using the magic of the Windows HOSTS file, directed this man’s computer to connect to my PC instead of the Unix system. My program would allow him to connect and work normally, as if nothing was wrong but, at the click of a button on my screen, it would interrupt the connection and fake a catastrophic core dump. Nothing was wrong with the server; it just looked as if there was.
It was like a magic wand. I could make him swear out loud and run full-tilt for the server room at the click of a button.
Having just written all this out I come to the conclusion that I’m much more evil than I’d previously thought. Oh well. Onwards and downwards.
At another job I had an “I got you last” contest with another employee. The “standard” joke was to slightly disconnect the phone cord to the handset and then ring the person. When she picked up, the cord would fall out.
Being on an air force base, we had those big old grey metal desks with a deep pen trough in the front. One day I stretched some rubber bands across the trough and made a paddle out of punch cards. (Yeah, this was back in the '80s.) I filled the centre section of the trough with confetti and would the contraption up. (I also had to tape some punch cards on the upper part of the inside of her desk so the thing wouldn’t snag.)
Then I unplugged her phone.
When she got back from lunch I rang her up. She picked up the phone and immediately discovered the loose cord. She plugged it back in. “Ha ha ha, Johnny L.A. You’ll have to try something else!” "Yeah, I guess I will,’ said I. We hung up, and then she opened her desk. I heard a loud rattling sound and a scream. Ya gotta love misdirection. 
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I have one of those very bright, blue-tinted LED flashlights on my keychain. A couple of months ago I got onto the lift with a co-worker. When she pressed the button for the ground floor I pointed the light at her hand and flashed it, saying “ZZZZZZZZT!!!” Ya shoulda seen her jump! I laughed and laughed and laughed.
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We’ve thought about getting a bunch of boxes and walling up the Director’s office with them.
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Since we got a new VP, people are nervous about layoffs. Traditionally, you know you’re in trouble if you go to your cube and there are moving boxes there. It would be a good joke to stack some boxes in someone’s cube (one person in particular); but that would just be too cruel, so we won’t.
I used to come in early and move everything around on the secretary’s desk. So when she would go to reach for the pencil…it would be complelty on the other side of the desk.
Also I would unplug her phone and tuck the wire under the phone so she wouldn’t suspect. So when the phone rang it took a minute (maybe even a missed call) before she could figure out what the problem was.
When I was forced to make coffee I would switch the pots so the decaf was in the regular and vice versa
I once had a stale jar of powdered coffee. I added just enough water to make a syrup. Then poured it in a little pool on a co-worker’s desk on Friday after she left. I propped a coffee cup to look like it had tipped to cause the spill. On Monday there was a shiny spot that looked wet like a coffee spill. But it was hard, and of course had lots of coffee in it, so that she kept having to wipe and wipe and it took forever to get it all up.
Take a co-workers chair apart and put tuna inside. Wait for said tuna to rot and for co-worker to go insane.
Pour Kool-aid powder into someone’s upside down umbrella. Wait for them to open it over their heads (preferably outside in the rain).
Get a similar desk calander to the one your victim already has. Keep switching them back and forth so they forget things they’ve written down on one calander or the other.
You really are an Evil One.
I like to shoot rubber bands across the cube farm. People never know where it came from. Heh heh, but sometimes it will come back. It’s great fun.
Turn a pair of shoes upside down and have the toes sticking out from under the front of your boss’es desk so everyone that comes into his office will think he’s getting oral satisfaction during their conversation.
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Clear tape on the phone mouthpiece. They will think that the phone is broken b/c no one can hear them. THen when they start to complain, swith it when they leave the room to the ear piece, now people can hear them but they can’t hear anyone else. Keep doing this until it drives them crazy.
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hair gel on the phone ear piece ewwwww
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rubberband the wheel of the chair to the desk, when they pull it out to sit down it will pop right back. That one is pretty funny forst thing in the Am
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Super glue the pens into the penholder cup. Particularly annoying when you are trying to take a phone message.
This one seems positively timid in comparison to some of the ones that are posted here. Ya know how it is when you get a song stuck in your head? Hum onene that’s particularly “catchy” (like Girl from Ipanema, The Chicken Dance, or the Theme from Mr. Roger’s Neighborhood). Do this for a couple of days and see how many people are randomly humming while cruising the corridors. When asked what they’re humming, most people won’t have realized that they were.
Tell ya what. I’ll add an entire thread of suggestions! Here’s the worlds greatest “reversable” computer pranks. !
Man, I haven’t pulled an office prank in years.
Back when I was doing temp work, I work for a company that processed Medicare claims. My department’s job was to open all the envelopes, flatten the claims out, and sort them. There were a lot of black ladies in my department, and mid afternoon they would all get their headphones out and listen to The Young and Restless on their radios, and discuss the show while they were working.
“You hear dat?” “Stella’s foolin’ around with Jimmy now!” “She needs to get slapped!” that sort of thing.
I worked at the same table with Belinda. One day while listening to the show, she started crying. I said what’s wrong? She said “It’s Mary. (snif) If she don’t get a new kidney she gonna DIE!”
That night I went home and looked up Y&R on the web and got Mary’s picture. I put together a letter on CBS stationary, put Mary’s picture on it, and typed out
Then I put it in an envelope and slipped it in Belinda’s drawer. The next day, she didn’t say anything about it. I decided to keep quiet so I wouldn’t be too much of a suspect.
Several days later, she was listening to Y&R and I asked her “So how are Mary’s kidneys?”
Belinda, a short 200 lb black woman, all the sudden slapped the table, tore of her headphones, gave me the evil eye, pointed at me and hollered “DID YOU LEAVE ME THAT NOTE???”
I just smiled and said “What note?”
She dug it out and hollered at me some more. I kept denying it. I THINK she bought it…
If you work for a large company that has multiple large restrooms which have multiple stalls within the restrooms…
there’s always the tried and true standard of anonymously turning the lights out on your way out when you know someone is squatting on the bowl.
Push back a desk at random intervals - just the tiniest bit. I had a woman here thinking she needed to go on a diet before she pushed her desk out again. So I started pushing it back in, but only on the days that she left work without notice.
Same woman, unplug phone from wall and only block the green wire. Phone rings - she can hear them, they can’t hear her. Went on until she brought in a phone repair tech, who immediately unplugged her phone (paper falls out) and plugs in. Tah dah!! Phone works and she looks silly.
Change screen saver password on her computer.
Move the furniture so that her back’s to the door.
Everytime she leaves the office, turn her office lights off - even if she’s just gone to the bathroom.
Sheesh! I just don’t like her, do I?
Oh I also duck-taped my boss into his office. He kept his door closed - so we cut about 100 strips of duck tape to door width then stuck them doorframe to doorframe. He had to use scissors to get out.
here are a few things:
in MS Outlook (if you use that) you can change the sounds for incoming/outgoing e-mails. Mr. Baboon changed mine to be farting sounds.
Take a sceen shot of your desktop and use it as wall paper.
Glue a quarter to the change return of the coke machine.
You guys are evil!
One that I remember from long ago, when I was a summer intern - we took the screws out of the bottom of someone’s phone, so the plastic cover was loose, then glued the cover to the handset. When he tried to answer the phone, the whole cover came with the handset.
At my current law firm, we had one really anal associate. Everything on her desk had to be perfectly arranged at all times. One night, another associate turned all the books on her bookshelf so the titles faced right intead of left (turning each book individually to preserve the order). It took her a week or so of feeling irritated every time she looked at the bookshelf before she figured out what had changed.
Another associate had been forced to do a project for a partner she hated. He got some writeup in a big bar journal, with a big mug shot. So another associate made about fifty copies of the picture, in various sizes, and hid them everywhere in her office. Pasted over the faces of her kids on their photos, slipped into the middle of her files, taped to her mousepad - he even put a tiny one inside the lid of her aspirin bottle. She was finding them for months afterwards.
I am always sending the lift up to the top floor, empty.
(people in the top-floor office are within sight of the lift door so they can see it open. but they can’t see into it so they wonder why no-one is coming out of it. they have to get up and go to it)
When I get to work tonight I am going to spend most of my hours wondering around the office(s) thinking/looking for ways to prank.
I might modify one or two highlighter markers (we use those a lot) so that orange comes out of the yellow marker.
Turn the alarm speakers up (we have an alarm that tells us something has ‘dropped’ it goes off a lot)
Putting red-dye in the water cooler would only make someone ask for a replacement (it’s happened before when we thought the water had a green tint to it)
One thing I do sometimes is never get out of my chair, I roll around between rooms in and out of offices. People arrive back from their fag-breaks to see me sat infront of the water cooler - “Lobsang you lazy bastard”
My step-dad and his friend would often play pranks. they had a colleague who was obsessed about pens going missing, and people borrowing his. He eventually tied his pen to his desk. My step-dad’s friend once replaced the string with a very very long piece, and then hid the length, so it looked like it was still the short string. then when this guy was at his desk step-dad’s friend would come along, say “can I borrow this, thanks” and walk out of the office with pen still on string attached to desk.
I’ll get back to you when I’m at work and have thought of some pranks…