IM ONLY USING CAPS TO STRESS THE POWER OF THIS PRANK....
buy like 10 really cheap battery powered alarm clocks from walmart.
and im assuming your in college, so wait till finals and then the night before his biggest final, sneak into his room and hide all 10 of those alarm clocks in really hard to find spots. now make sure you set each one to go off about 45 minutes after the last one so he will just start to fall asleep when the next one goes off.
he'll wake up the next morning tired as hell and severly pissed off and most likely do bad on his final. spending a whole semester in a class and trying hard in it only to fail it at the end is one of the most brutal paybacks i could think of...
let your finger nails grow out a bit then pinch him.
or just bite him
get a saudering tool and sauder (sp) is door lock together and lock him out, and this was the key wont work
you could always piss on his door handels, in the winter it works better .... and jam some poo, your own works best, as human poo is uber gross, under the door handels. then try pouring fish juice into his air intake vents. the car will stink like fish and he will have to touch your poo. that should do it.
you probably dont want to claim this, I did it to a friend of mine, and later he filled my back pack with shit. just befor we left on a trip. peace was then established, as the next step probably involved giving some one aids.