Here is a classic which has been fading into a lost art. It works extremely well someplace like a military academy or such, where everything must always be in impeccable order, but can be used for good effect in a dorm room, too: ©OFFICEJOKES.NET

It's the fine art of stringing up a room. The idea is to string the room (trough makeshift pullies and levers, etc.) such that as the victim turns his door knob and opens the door, his entire room is upset. One classic example involved stringing the bunkbed so that it lifted itself up of the floor and turned upside down, books would tumble off a shelf, in turn moving a dresser across the room, emtying a wall locker, pulling the shoes up into the light fixtures and otherwise creating serious havoc.©OFFICEJOKES.NET

What's nice is that the destruction itself is done by the victim; all you did was run a little string.... This, however, can lead to serious counter-pranks. Don't say I didn't warn you!