It was funny reading some of the remarks and suggestions here, but as vnv727 mentioned, you don't mess with another person's car. It will only make a much bigger issue.

Try the sensible approach first, and gradually if it doesn't have an effect, you can 'justify' taking it to the next level.

Correct! It is funny however to think about all of that funny stuff . I gotta guy that repeatedly let is lion-size dog relieve himself in my yard, off of the leash. Asked this Frenchman repeatedly to cut it out. Didn't. Last time I shoveled it up, walked down to his house and pitched it onto his front porch as he watched. Hasn't happeded again. Point is, be a nice guy until the moron proves he's not capable of understanding your compassion. Then consider a more DIRECT communication.

Wish I could of been there... Priceless.

I still think ringing doorbell and telling him you are not gay so stop the car whistle is the best option. Then he will feel like a douche!

I like the idea of telling him that you are not gay........and be sure to tape it so we can all see his reaction.

hahaha i like this one

but really you should just talk to him first like many other people have said..
if he doesnt stop after that.. use the airhorn
if he still doesnt stop kick him in the sac and when his head goes down to grab his ***** knee him in the face
then its game over

put a NAMBLA bumper sticker on the back of his car (does NAMBLA havebumper stickers? i guess if you bought one you'd be supporting them, so maybe that's not that great of an idea)

If you can get your hands on a paintball gun just sit outside his house shooting his back window until he comes out. When he's out, pop open a beer and keep shooting even while he's yelling at you. If he runs at you just point the gun at him and he'll stop, then go back to shooting his car.

Or just cover his entire car in rainbowpost-it notes