My wife was reading a message board which was set up by a student where she went to college. She found a thread where people posted different pranks they pulled at the school.
One of the best ones:
Every year, they have a day where high school seniors come and check out the college. They stay in the dorm rooms and shadow some of the college's students.
Before the high schoolers all got there, one of the rooms cleaned their toilet extremely well and they drained all the water out of it. Then they poured several bottles of Mountain Dew into the toilet and tossed a couple of snickers bars in.
Now, this particular college is known to have some extremely strick rules for the students. They have room inspections daily and the rooms have to be spottless.
Anyway, one of the roommates (a freshman) was sitting alone in the room reading while the other roommates had taken their freshman students around campus. They got back into the room and the senior roommate went into the bathroom, came back out and started yelling at the freshman roommate. "YOU DIDN'T FLUSH THE TOILET AGAIN! YOU KNOW WHAT THAT MEANS!!!"
The freshman then got up with a look of remorse, went into the bathroom, and stuck his head in the toilet to fetch the snickers.
From what the person posting said, the high school students never came back.