EEEEeeeeeewwwww!
We had a guy in our house in college who thought it was funny to whiz in the Apple Juice and put it in the fridge...he got fitted for new teeth that year! lol
I habitually scared people. It get to the point that people would visit with my roommate and would look in closets and behind doors, etc. to preempt the scare. At work I'd staple pant cuffs to uniforms and watch a coworker attempt to step into his pants and fall over...or the time I filled his work gloves with liquid soap...or smeared grease on the telephone and call him from the other room, he'd have a black streak on his face.
In highschool I used to chew tobacco (disgusting, repulsive habit). I was using a soda can for a spitoon and left it out. My father picked up this full can and thinking that somebody opened a can of soda and only took a sip from it, he placed it back in the fridge. --where my brother saw it and decided nothing better than a cold swig of rootbeer.
Yeah, that's a memory that stays with me!