Ok here is the most evil practical joke ever (from college).

Explain the following evil bit of physics to your non physicist roomate.

1. Hook up a high voltage generator to a piece of tin foil on one lead and a wire on the other. High voltage, no amps. You just want a big potential differnence. you don’t want permanent injuries.

2. Put the tin foil underneath the bathroom rug and the other lead into the toilet tank.

3. Explain that ions in water are what carries current and that by standing on the carpet, he will have a lot of electrons stripped off of him. When he pees, he will complete the circuit and get them back.

4. As your buddy considers this explain the pain of an electrical arc bouncing up his stream to a private place.

5. Mention that it is no problem, because a voltage generator would be easy to detect from the red on light and the loud hum.

6. Put a remote controlled box with knobs and dials in the bathroom off to the side… make sure it hums.

7. Turn it on when your roomate groggily goes in to do his morning thing. He will see the red light, hear the humm and jump.