Go to the parts store and get a valve core remover tool and take the cores out of his valve stems leaving the tires flat.
Get really long zip ties and put them around the cv shafts if its front wheel drive or driveshaft if its RWD.
Lotion on the underside of the door handles so his hands just slip off.
Get a bar of soap and rub it all over the windshield so when he uses the wipers it just foams up and makes a shit ton of suds.
And then saran wrap the fuckers car like crazy. The key is to not damage his car in any way that he could get the cops involved, but you want to go over the top so he knows he's your little bitch when it comes to fucking with cars. Just make it as miserable as possible for him.