Hmm, I would suggest just placing the vaseline under the windshield wipers, make for a nice surprise next time they use em. Also, milk smells horrible after it has been in a hot car for a few days, so it might work nicely in the vents. You could also cover the car in vaseline and grab as many as the free aol type cd and stick them on top of the vaseline, covering the whole car. Could also get some of those little glass stinkbombs, I am sure you could easily figure out a few good things to do with them. If nothing else, just mix up a big bucket of mud and go to work covering there whole car with it, just be sure to slap it on instead of wiping it around so you don't scratch up the paint. You could also pour a bunch of oil around on the ground under the car, just to freak them out. Can't think of anything else right now.