Just remembered a great prank I did.

Mum had a bunch of the little strip of cardboard that goes bang in Christmas crackers. You use them to make your own but I got hold of a few. I taped one end to my little bro's door and the other end to the wall beside it. The next morning I got up early before he was awake and knocked on the door. He went to open the door and it went BANG in his face. He was pretty shocked.