After your sure of who it is stick a dead fish under his driver's seat in the car he drives if it is his and not his parents. After a day or two in the hot weather, oh boy.
Another thing is other than grabbing the keys if he leaves the car running, just sit in it until he gets back. I doubt he would try and drag you out of it.
Go talk to his old man, tell him what kind of a jerk he spawned.....
Good luck either way you go.
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