Position a Van de Graaff generator near a door so the next person through discharges it.
Science geeks at their best.
We bounced lasers off a slow rotating mirror in the hallways.
When people walked by they would see the beam without really worrying, but we would wait till it got a few feet from them and yell, "Don't let it hit you!"
Fun to watch them throw their books and tuck n roll.