We did the penny trick many times. After my roommate and I were locked in our room for two hours while everyone else was out drinking, I stole a pipe wrench from the utility closed. Until the end of the year when the lock snapped, it gave me just enough leverage to unlock the door.
Did the talcum powder in the ziplock bag.
I always wanted to drag someone who was passed out into the elevator and just leave him there. Never did, though, because the school started cracking down on underage drinking, and the person likely would have been arrested if he was found.
Completely sealed off one doorway with duct tape, while the guy was inside sleeping off the night's party. It would have been funnier, but he was still pretty groggy when he woke up, and ran smack into it. A nice chunk of his hair had to be cut off...
Our dorms had "rape alarms"; in every shower stall, there were strings attached to the alarm that you pulled if someone attacked you. Late one night, we tied all of the strings to the shower curtains two floors above so that the alarm would be set off when the curtains were opened. The next day all of the rape alarms on campus had the strings cut short
We had an ongoing "war" with the guys two floors above us. After an incident one night where one of them relieved himself on our bathroom floor, we got even. We filled a few monster-sized garbage bags with snow, and coated part of one wing with snow 6 inches deep.
A gallon of concentrated dish detergent from Sam's Club emptied into the fountain...enough said
Our dorm had very heavy bunk beds that were difficult to move. One morning, we noticed that one of the guys must have been in a hurry when he left for class; he locked his door, but hadn't latched it. We pushed it open, unlocked the door from the inside, and pushed the bed close to the door. We tied nylon rope to the legs, dragged the bed against the door, and then shoved the rope back underneath. It was hilarious, sitting there watching him locking and unlocking his door, trying to figure out why it wouldn't open.
Another night the same guy passed out in the bathroom without locking his door. We disassembled the beds and removed everything from the room. He came to a few hours later and opened his door, only to find his room completely bare.
My current roommate once passed out on the floor of our bathroom. We stripped him down to his underwear, and left him in the girls' bathroom upstairs.
My dorm was right across from the football stadium, and my window faced the entrance. A super-soaker on Saturdays as people were leaving provided endless entertainment.
To anyone in college: if you choose to drink, ALWAYS LOCK YOUR DOOR WHEN YOU PASS OUT. My roommate and I woke up one morning to find ourselves duct-taped to our beds.