alright there are a few ways to look at this.
You can get him back, but be nice about it. try:
1. KY jelly on the door handles
2. Condoms filled with just the right amount of water and mayo
3. Toilet Paper all over the car
4. Power bars on the tires ( put one or two on two of the tires. they think that they have a flat cause thats exactly what it feels like.
5. Oatmeal on the windshield, get it a little wet but not so soaked that it runs off
6. Saran wrap it obviously
7. if you have jacks and jack stands you can turn the car around from where it was ( harmless but funny as hell when they go out and the car is backwards.
8. i just saw another idea this morning, put different colored sticky notes all over the car just like this:
http://www.stumbleupon.com/toolbar/#url=http%25253A//www.groundproject.com/uploads/postit/index.html
(sorry if it wont click)
you can butter the floor in the kitchen or entry and see them fall
Another funny thing to do is talk with friends of his about doing terrible things to get back at him and say when youre gonna do it. When he doesnt sleep over the fact that you might fuck up his car, put a note on it saying
" Sucks staying up all night worrying about what might have happened doesnt it? love, (your name)"
(that happened to me i was getting a kid back for tagging my bros car) and then get him back like a week later when he thinks its all over
OR you can be a douche about it and put bologna on the car and shaving cream and shit. its up to you,
all the ones up top are safe for the car and paint and shit so theres no damage