A coworker once pranked his coworker at a previous job-- the victim had to do lots of stapling one afternoon, frequently interrupted by trips to the copier or somesuch. My prankster friend would, upon the victim's departure, remove all but a few staples from the man's stapler. The guy came back, stapled a few pages, ran out, refilled his stapler, and continued. Naturally, my friend kept removing most of the staples whenever the victim left, but for some reason teh victim never made note of the fact that he was constantly refilling his stapler.
When my friend the prankster finally let him in on it, exasperated by the failure of the victim to catch on, the victim just told him, "I dunno, I thought I had a low-mileage stapler." Heh!
I always wanted to do more pranks.
Mostly of the harmless variety, not of the cruel hidden-camera variety. I mean, if you think there's an axe murderer outside, of course you're going to freak out. But what if a cell phone was going off and you couldn't find it?
But to prank people and get away with it, you need social capital.