When I was in high-school my teacher used a projector to show us a couple of slides. She projected this on the whiteboard since we had no real projector-screen. When a student asked a question that demanded her to draw something she would block the projector with a book while she used the whiteboard.
So this guy sits at the back – by the projector. He never usually talked much. He raises his hand. The teacher takes a few moments to realize he wants to say something and gives him the word. He goes
“I’m really sorry, but I just want to say, that the book is on fire.”
The class turns around towards the guy – and right beside him – the book is totally LIT UP – having been set on fire from the light of the projector. Teacher goes crazy and starts screaming. Bunch of people is laughing or running around. In the end someone gets out a fire-extinguisher and sprays it all over the classroom. This all resulted in a damaged projector, foam-filled room and a short day.
Best class I ever attended.