Keying cars is a really pussy, passive aggressive move.  If you are really steamed up, do as some of the others have said and get him towed.  Or get some friends and box him in for a while and see how he likes being inconvenienced.  \n\nSeriously though, vandalizing someones shit isn't very cool.  It won't bring this douchebag down to earth, it will just bring you down.