This one is possible in two situations: Either the kid left his windows down or you have access to a key to his car. depending on your level of access, do you best to fill every single inch of the vehicle with either shredded paper, ping pong balls, or packing peanuts. We're talking about inside the glove box, in the ash tray, even in the CD case (oh wait, those don't exist anymore).

If you're feeling extra sneaky, pop the trunk lift up the spare tire compartment and fill that, too. Imagine their faces when they go to fix a flat months later and find a bunch of crumpled up news covering the tire. Each one presents its own issue: Tiny, painful cuts from the shredded paper, the danger of creating a mini ping pong avalanche when you open your door, or the hassel of those tiny styrofoam scraps from the peanuts. Any way you choose, it's going to be a hassel to clean up.