What I used to do when I was an angry little punk (but was heavily into the automotive scene here, so all my revenge plots were car based...which sounds like it would work for you) was buy aircraft remover and pour that all over the car which will strip the paint down to bare metal. It also eats light plastic and thick rubber so do with that what you will.
Another thing I used to do was remove peoples valve stem cores with a little valve stem core remover you can get at any decent auto store for like $3. After you take out the valve stems the tires will deflate super fast so you have to rush to put the cap back on before they loose all the air and look like you did something to it. Only put the cap on slightly, when he runs over a bump the air in the tire will be to great for the valve cover and the tire will almost literally fall off the rim from the pressure. Hard to get it to work properly (usually just looses are super fast and they get a flat tire), but when it does its amazing. If anything they will be confused as hell because almost no one knows you can just remove someones valve stem. Most people spend forever trying to either A) inflate the tires again, which is impossible because the air will just rush back out, or B) buy new tires.
Something that is simple and easy though is smashing in just 1 of his windows (NOT THE WINDSHIELD) because it will cost about $200 or so to fix per window, and peoples deductible on their insurance is about $500 so that is all out of pocket money.
Finally, if you have a small amount of automotive know how you can pull his oil pan drain plug, let most of the oil run out of it (into something you can take away so he wont notice a giant oily mess under his car), plug the hole back up and hope he drives it around for it a bit. If he does not notice the oil light fast enough and pull over he can destroy his engine.
All these work, just depends on how big you wanna go.