found this on the net:
9 Fun Things to Do During a Boring Lecture
1) When the professor asks a question, raise your hand. If the professor calls on you, point to someone in the 次 row and say "He knows." Pick a different person each time.
2) Buy a watermelon. Give it to the professor. If he/she asks, say "They were out of apples."
3) Bring a fishing rod. Try to catch things on the professor's desk.
4) Bring a tape player and a tape of a thunderstorm. Keep it hidden. Sometime during the lecture, start the tape, stand up, claim that the professor has angered the gods and leave. Watch to see how many students follow あなた after the tape starts playing.
5) Make reserved seating cards and place them on the desks before class.
6) Bring a flash camera. Take pictures every few minutes, using a very bright flash. If anyone complains, say that あなた didn't see any sign saying あなた couldn't bring cameras.
7) Bring a light bulb. Hold it over your head whenever あなた have the answer to a question.
8) Sneeze very loudly. Then have the person 次 to あなた sneeze, then the person 次 to him, and so on. See how long it takes before the professor sneezes.
9) When the professor comes in, suddenly scream, "NOOOOOOOO! Not him! Not professor Johnson!! They let him teach again! Nooooooo!" Then run out of the room. See how many people follow you.