Scored three huge pranks in college, when I lived in the dorm at UF. First was a water filled weather balloon in a room. When the student came home, opening the door pushed a stick with a nail on it, into the balloon. Water cascaded down 4 stories. Second was charged capacitor taped to the underside of the urinal in the communal bathroom. Wire from that to the bowl. Another wire to a puddle of salt water on the floor. Peeing completed the circuit. Third was a ceiling light bulb in a room. Broke that, attached a cherry bomb to the filaments. A large ketchup filled bag was taped to that. Turn on the light, everything in the room is coated in Ketchup.
