When I was much younger, I once put warm apple juice, in an easily-knocked over cup, on top of the door. Next nurse that walked in...
That was probably one of the most mean-spirited pranks I ever pulled. Ha. Later, I stayed unbored by talking on the phone, playing games on my Palm handheld (they're such wonderful little devices!), watching TV, and chatting online if I have net access. Now I don't usually go into the hospital at all, but inject antibiotics at home.