I've got a ton of these stories...
Biology class. One of the people in my lab group was THE most popular guy in school. I made him cry. We were dissecting crayfish. Amazingly, he was doing most of the work. As he worked, he cut away any parts of the crayfish that he no longer needed, including the extra claw-arm thing. I was playing with this ice-pick type tool. I stuck it in the crayfish's arm and was swinging it around like a party favor, ya know like one of those things people swing around on New Year's Eve. Then this kid stopped for a minute, trying to decide what part to go after next. As he thought, he set his hands down on the table. His right hand formed a perfect cup shape. So I dropped the claw in his hand. He blinked, looked at the claw in his hand, and SCREAMED BLOODY MURDER. He yanked his hand away from the claw and RAN away from the table to the other end of the classroom, screaming the whole way. It took him about ten minutes to get himself back together.