One very cold winter day in college, me and my friends filled another friend's car full of snow. That's the worst that comes to mind. Later, the same guy was trying to do his laundry and every time I heard him put the coins in the dryer in the house, I would go and open the door on the machine to stop it. It took him several hours and lots of quarters to dry his clothes.
My best buddy in college we used to prank relentlessly when he passed out -- write on his face, put toothpaste on his hands so he got it all over himself while he slept, wrap him to the bed with saran wrap. I stopped someone from shaving his eyebrow though, that's going too far.
In high school, one of my friends drew a big afro on another guy's driver's license picture in permanent marker as a prank. That actually looked pretty cool. Also in high school, a bunch of us were hanging out and we called the RCPD to report one of our friends had jay-parked (parked facing the wrong way on the street). The cops didn't really want to come out and give him a ticket, but they did. He was pissed.
I've been part of a lot of pranks, but the most ridiculous things I probably did to myself when I was drunk...