A friend of mine's father is a doctor and while in med school had a favorite prank he'd pull. During dissections, he would tie some fishing wire to a certain appendage of the subject, and then suggestively yank the cadaverous penis at inopportune times -- much to the surprise and dismay of a certain female lab partner. Funny? I think so. Sick? O God, most definitely.
Also, I have my own critters. Namely, a small contingent of very large black ants. They show up mostly in the kitchen or bathroom, occassionally straying onto the living room floor. Normally, I'm in the not hurting any living thing camp, but I get mean (not THAT mean) when I drink whiskey and I like to smash 'em with my thumb and forefinger. It doen't help though. I cannot singlehandedly keep their numbers down. I hate those ants.