* A friend of mine at U of Chicago once calculated the resonant frequency of his dorm's stairwells, bought a test record with that tone on it and played it into the stairwells from a number of stereos. Apparently had the entire building shaking visibly before they got scared enough to turn it off.
* When living in the dorms, I offered to make soup for everyone on a Sunday night (when dorms don't usually serve a meal). I made the soup in a toilet bowl, using several of those coil cup heaters. Looked good, but no one tried it.
* I had a friend who lived in a room next to the study lounge. The night before finals, I invited him up to my room and then phoned his room, letting the phone ring until the angry mob in the study lounge broke down the door and ripped the phone off the wall.
* Someone was foolish enough to penny me into her own room. Amongst other things, I placed a call to the US Embassy in Nepal. The call was completed and rung back some time the next day.
* Ran an imaginary student for a student government position. He was named after a dog. He didn't actually make the ballot because his false ID was discovered by the administration, but he still won on write-in votes.
* I had a white cane and dark sunglasses, and I would go with a friend of mine to a Mall, where he would lead me around as if I was blind. However, he would be deliberately cruel, leading me into pillars, telling me the wrong number of steps, and so on. People would get very upset.
* I once learned the day before that a professor would be late to one of his classes the next day. I made up a "pop quiz" that was incredibly hard, and then showed up and handed it out to the class, telling them that I was a grad student the prof had sent to proctor.
* A friend and I put on surgical greens, masks, booties and so on, and then splashed red food coloring on ourselves. Then we burst into the medical library, arguing loudly, and go over to the reference copy of Gray's Anatomy. I leaf through it, peer at a picture, and point and say triumphantly "See, I told you it was on the left side. What are you, dyslexic?" My friend looks abashed, shrugs, and we walk out.
* One that I never got a chance to do: Wait until someone brings a cute little puppy on to campus. Then, later that day, rush onto the dorm floor with the puppy wrapped in a bloodstained blanket. Explain to everyone that the dog was hit by a car and it has a large sliver of glass in its side. You don't think it will live long enough to get it to a vet, so you're going to pull the sliver yourself and try and stop the bleeding. Go into your room (with the pet owner) and close the door. Play a previously prepared tape of a dog whining and barking in pain, and say things like "Jesus Christ! Hold it still! Oh, shit, I'm going to be sick. What the hell is that?" and so on. (I couldn't find the sound effect on the day the puppy was there.)
Those are the ones that come to mind off hand.