I can’t really think of anything that isn’t at least a little bit obscene. The whispering in peoples’ ears is a good one though.
“This is GOD! Now, here’s what I want you to do…” 
Another thought struck me though. If you were invisible AND dying, where would you choose to leave your decaying corpse? I can’t quite decide.
I am invisible, and I’m having plenty of fun making Homer think his house is haunted. Tonight, I think I’ll get under his bed and make it shake like in the Exorcist. That should be fun.
Disney World. If possible I’d have a friend chop me up post mortem and distribute small invisible bits throughout the more irritating rides so as to finally shut them down.
Oh, and before death? Um, the locker room thing and the nasty pranks thing, thats about it though.
First, I’d run over to the nearest skyscraper and hang around in an elavator. When someone came in and hit the button for their floor, I’d hit the one for the floor just before the one they want. After the doors closed.
Then I’d visit an organization I didn’t care for and use their hard cash to make a donation to one I supported.
Then I’d hop a plane to Tahiti and stay there for a bit. Maybe get in some good birdwatching.
I’d have to do this all in sandals because my feet are REALLY tender and I’m helpless once I get outside without footwear.
Oh, Boo-Boo, I always knew it was you, oogly-bear!
–Tim
I’d hang around in various PHB bosses’ offices at work during the day sending e-mail to everyone announcing intelligent decisions. I would whisper evil things in their ear so they don’t know whether to believe me or the voices in their head that have been telling them to do boneheaded things.
I would board lots and lots of planes and hide behind the attendants at the end of the flight and in between the buh-bye…buh-bye" I would scream in a falsetto voice “TAKE ME NOW YOU BIG HUNK OF MANHOOD, YOU” at unsuspecting people exiting the plane. Especially if the attendant is male.
Just silly little things to keep me entertained…
Invisible? Me?
YOUR WORLD WOULD AT LAST BE MINE, PATHETIC EARTHLINGS! :evil laugh:
:ahem: I would do. Seriously, I would actually try to conquer the Earth. I would start by convincing stratigic pawns that I was a god. Once thoughly brainwashed my worshippers would begin converting the unbelievers while I proceded sowing chaos among my foes and attaining control of strategic resources.
I would also begin recruiting for my ruling class, starting on this message board. I would of course take control of any chemical needed to keep me sane, not that I am…
Old people are already often invisible.
I know most of these have already been mentioned, but here’s what I’d do:
Be the voice in crazy people’s heads. Run 'round in the nude. Peek at the wimmen. Sneak into ______ without paying. Be a poltergeist. Murder-for-hire (it’d be a lot easier that way than it is now…oops…5th amendment!). Lots of other crimes. Get free food. Be someone’s real invisible friend, and beat up th people that don’t believe in me (wasn’t this a Far Side cartoon?). Steal stuff.
Under the bed of someone you hate.
“What’s that smell?”
“Sure as hell not me.”
“Well, it’s something in this bedroom…”
I’d wait around at places where there are long lines and trip anyone who cuts.
I’d also hang out at the grocery store and when anyone had more than the allotted # of items in the express lane… I’d pick up their extra items and throw them off the conveyor belt.
Small things, folks, but small minds – wait, that’s not how it goes…
Well, so are fat middle-aged women, but you don’t hear me complaining 
Of course, if I were really invisible, I wouldn’t have to worry about my weight anymore. I also think it might be fun to sit on people’s laps at the movies.
Catrandom
**
GIF!! GIF!!1!
Sorry, that was lame but entirely called for IMO.
I already know what friends think of me due to being half-asleep-half-awake when they disclosed their feelings about me to one another (on multiple occasions), and now that I’ve discovered this “een-er-net” thing the prospect of women’s locker rooms seems like a waste. So I’d probably just put all the kitchen chairs up on a table when the family turned their backs, or pinch people’s behinds in order to start fights, or other childish pursuits.
I prefer to daydream about more realistic things, like weighing more than 140 pounds soaking wet, or playing 2B for the Phillies.
“Hey, why are all the Laker girls jumping around on the sidelines like they’ve been goosed?”
I’d be pink.
And I’d be a unicorn.
I’d be worshipped.
Threads would be composed about me.
I’d rock.
Chief you already rock.
I’d satisfy my curiosity by visiting lots of places I’m not currently allowed to go. After that, I’d work on projecting an invisible force field…
?
I’d bump into things a lot. Oh, are we talking about some form of invisibility that allows vision through invisible eyes? Cool, I always wanted that kind!
I’d haunt televangelists on the air until their followers were convinced they were tools of the devil.
I’d go anywhere that looked interesting, and find out anything I pleased.
I’d strike fear in the hearts of PHBs everywhere…if I could find some with hearts. Otherwise, I’d strike fear in their colons or something…
I’d go out nude. Not only would people not point and laugh, I’d be immune to sunburn!
I, too, would be someone’s invisible friend. Preferably an attractive adult female someone. Depending on how shy she is, I might mimic a female voice so that she wouldn’t feel so uncomfortable undressing…
I have seen a lot of good comments, but what I would do if I was invisible is this. I would sneak into the offices of various high-level officials in our government and expose them for the idiots they really are. Carry a small recording device or a digital spy camera, then send the tapes and pics to the papers.
Then I’d go over to the papers and drive the editors completely nuts until the published the photos.