A group of roommates triple-stacked their beds. Before they decided to take the beds down, they wanted a picture taken with the beds stacked. Three of them rig the middle bed not informing the 4th roommate. (he even gets a running start)
Another excellent submission for our recent college contest. After getting a bucket of water dumped on him, one college roommate decides to strike when his friend least expects it: while he's asleep.