All of the suggestions about sending stuff to their house probably wont work. I bet the little gits live with their parents. If you dont live around there, then revenge will be a sweet way to go. Use superglue on the locks. Pour rancid milk in the heater vents near the windscreen. As the summer is coming they will need these. We all know what its like here, it gets hot and rains, so you cant open your windows, and you have to put the blowers on. When they do this they will get a nice puke smell which they wont be able to get rid off unless they want to dismantle the heater matrix. This is a tried and tested method, that I used to wreak my revenge on some old next door neighbours of mine. If you have enough bottle you could report the car as stolen or say you witnessed them holding up a garage.