Here's a really mean trick that you can play on people waiting in the dentist's office. I recently had my wisdom teeth removed and had an appointment for a check-up to see how my mouth was healing. So naturally, in the oral surgeon's waiting room, there were people that were going to have some dental surgery and everyone looked pretty nervous. Except for I, of course, because it was only going to be a brief appointment (5 minutes or so). So after the check-up, I stuffed some Kleenex into my mouth, opened up the door to the waiting room, and announced loudly to my waiting father, "Boy! that was the fastest tooth pull they've ever done!"
The expressions on the patients faces were priceless. And my father thought that what I did was extremely evil. Try it! You'll like it!