Take a sweatshirt and spell out a date (any date, your birthday maybe) on the front with contrasting tape. Wear dark glasses. You are a blind date.
Get an old pair of jeans, cut out the seat, and paint your behind blue. You are a blue moon.
Find a good headshot of Kevin Bacon on the web. Print it out and wear it as a mask. Cut a bunch of ovals from white paper and tape them all over your clothes. You are Bacon and eggs.
Find a good headshot of Jack Nicholson. Print it and wear it as a mask. Make or buy red horns, pointed red tail, and red trident. You are devilled ham.
Get a sheet of posterboard and some woodgrain shelfpaper. Apply the shelf paper to the poster board and wear it as a large tube around your torso. In large letters write “Property of J Kirk” on the outside of the tube. You are the captain’s log.
Wear white clothing nad make floppy ears out of sox. Apply the appropriate make up. Act seriously ill. Tell everybody “They really ARE for kids.”
The easiest, cheapest and most effective costume I’ve tried recently required about $5 of gauze bandages. Just wear a black sweater, black pants, black shoes and an old black hat; a black fedora is best, but anything will do. Wrap the gauze around your face and neck, covering them, and slip on a pair of sunglasses and black leather gloves. You’re the Invisible Man.
And it looks great.
I once knew a girl who dressed up in a black leotard with little metal objects pinned all over it. She was someone with a magnetic personality. 
These are all awesome.
Get a bunch of maps of Massachusetts, shred them and apply the shreds to your body. You are a Mass Murderer.
Counterpoint: Shred a few empty boxes of Cheerios, and apply the shreds to your body. You are a cereal killer.
The cereal killer can be accessorised with a hockey mask, fake knife and a box of cereal covered in fake blood.
Get some pieces of fake fur, wear ripped old clothes and stuff pieces of the fur thorugh the rips. You are a were-wolf, halfway through transforming.
Wear a tux, carry a gun and a martini glass. You are James Bond.
Wear a suit, red braces and a blue shirt. Carry a pack of tarot cards or a crystal ball. You’re in “futures”.
Get some fake mice and attach them to your shirt. You are the rat race.
I’m reminded of the scene in “Three’s Company” where the late John Ritter had taken some medication, then donned a tux and went to a high class party. He did an astonding dance number, ended up dancing on the bar and then fell behind it, and came up slowly with a huge potted plant on his head. The moment where his eyes appeared was one of the biggest laughs on the show.
What a great physical comedian. What a great costume.
If you like beer, go as Guinness! A friend of mine did that a few years ago - wear all brown clothing, then use white paint from your nose up, and spray your hair white.
Not as cheap, but same year another friend went as a deviled egg - she dressed as a big hardboiled egg, then added a tail, cloven hooves, and devil ears. The effect was surprisingly creepy.
Black tie. Slacks. Cheap cigar and rumpled raincoat or trenchoat.
Go as Peter Falk.
Well, my idea isn’t a pun, but I hope you’ll hear it anyway.
Redneck Dracula-- Flannel shirt with the sleeves cut off. Long underwear shirt if it’s cold. Trucker hat. Enormous belt buckle (The one I got from Goodwill has cowboy boots and crap on it). Cape. Gaudy Jewelry. Maybe some facepaint if I’m not too lazy.
Maybe it’s more of an anachronism?
I think it was in the movie Philadelphia where Denzel Washington, playing a lawyer, came to a halloween party in a suit with all sorts of laws clipped from a law book taped to it.
“I’m a lawsuit.”
My friends and I have a Firefly themed party this weekend, one of the girls is going to wear a dress and combat boots (she’s going as River), another one is going to wear overalls with a teddy bear embroidered on them (Kaylee), and I’m trying to find another person to wear a business suit and blue lab gloves (We’re going to go as the Blue Hands Group)
I like the redneck Dracula idea! I’m not necessarily looking for a pun, just something that’ll be appreciated by the most people while necessitating minimal cost and effort on my part. 'Cause sometimes I’m lazy like that. I love the premature ejaculation thing from page one, for example, but I’m gonna nix it because a) it’s too damn cold to be wearing only jeans (and the place the party is being held has a gorgeous rooftop area), and b) it’s too pun-ny. I’ll end up having to repeat the joke umpteen times, which I’m sure will pall for me and everyone else.
An ideal costume would be something that’s unmistakably entertaining and costume-esque on site, and which is then improved upon explanation.
Strip naked, roll yourself in powdered sugar. You’re anthrax!
Wow.
If you are the right build then perhaps you can go as a gnome. My friend and I dressed up as gnomes last halloween and it turned out pretty good. We got witches hats, cut off the brim and covered them with red felt for hats. We wore black sweatshirts with a thick leather belt around our waist for our tops. For the pants we just had on some baggyish khakis and then some cheap foam type black paper for faux boots.
He was a perfect gnome becuase he was about 5’6"-5’7", a solid 190 pounds and a Sikh (I believe) so he had never cut his beard. I, on the other hand looked fairly stupid becuase I was 6’1" 195-200 athletic pounds at the time. Plus I had to wear a crappy fake beard that didn’t look good. I might be able to dig up some pictures if you want to see them.
Get a scythe (fake, of course, unless you happen to have a real one laying around), a plain blue shirt, and a marker capable of writing on the shirt. Write the error message you get when Windows crashes and goes to the blue screen. You’re the Blue Screen of Death.
Or just dress in all black and wear a black beret. Go as a stereotypical snooty French philosopher. (Cheesy fake accent optional.)
Or go to the Salvation Army and look through their racks of ancient clothing. Find something that is clearly from the disco era and buy it for the $2.00 or so they want for it. (This is what I did for a New Year’s Eve party one year. The theme was “the 70’s”. I think I spent $10 on the entire outfit.) Not particularly creative, I admit, but it’s cheap and easy.
Get or make a hand puppet of the president and go as the vice president. (Also works if you want to go as Karl Rove.)
Go to the store and buy a dozen or so cans of SPAM. At regular intervals, hand one to another party-goer while yelling, “You’ve won a free iPod!” or “Get hard for her today!” You can also print out actual junk email you’ve recieved and tape it to the cans.
I really like both of these.
Oh, and for reference purposes: I’m 6’3", 200 lbs, kinda geeky looking. So probably not the right build for a gnome, although that’s a cool idea.
That’s awesome! I’m suggesting that to one of my coworkers (he originally planned to be Groucho Marx, but he’s having trouble finding a swallowtail coat).