man there are so many pranks....
have you ever heard of "pennying" someone in their room? Get 2 buddies and a bunch of pennies. Have your buddies lean all of their weight against the door (while the person is sleeping in the room or something) and it will create a small crack between the door and the doorjam. Force as many pennies into the crack as you can, it should be VERY tough to put the pennies in because the crack is very small. This puts a large amount of force on the door in the doorjam, and when the person inside tries to turn the door handle, he/she can't because the amount of friction is too great between the little thing that sticks out of the door that goes in and out, and the socket it sticks into in the wall. Sorry I am not great at describing these things.
Get a HUGE freezer bag and fill it with shaving creme and really smelly stuff. Go up to someone's door and slide the open end of the freezer bag under the door. Then drop a book on the bag :laughing BOOM stuff explodes out of the opening and goes ALL OVER the person's room. It is funny, and they can't avoid it unless they know it is coming.
Fill a garbage can up with water, lean it against someone's door, knock, and run.
Take a couple of crickets and let them out under someone's door, they won't sleep for weeks.