Let the air out of the car's tires and refill the tires with R-22 or R-134 refrigerant (make an adapter hose) until the tires are soft and look like they need air badly, but can be safely driven to a filling station.    When the driver gets to the filling station, the heat generated in the drive will have caused the refrigerant's pressure to increase so the tires won't appear to need air anymore.  If they're checked, they may in fact be OVER pressure, and he'll end up letting some out instead, which will make them sink even lower when they cool off.

Fun for days!

Capture some ants (preferably fire ants, if they're available) and throw them in the car
along with some food for them. Cornmeal and sugar.   They'll establish an ant colony under the car's carpets.

Wear head to toe protective clothing, grab an active wasp's nest, and throw it in the car through an open window.

Wrap a coat hangar in the U-joints or around the axle shafts.  Not harmful, but makes alarming noises.

Trap and release rats in the car.

CJ

Oh hell, just kill them.

I've heard of people using musk or other animal scents from a trapping supply place. There is a magazine called Fur, and Feather that is for trappers, probably could order through them or go online.

From what I understand they would pour or squirt the scent (the nastier the scent the better, musk rat urine, skunk, etc) into the outside vent of the offending vehicle. When the fan/heater is turned on it will blow it through the car. Another way is to apparently use a syringe and inject it directly into the car through the window weather striping.

I've heard of people even supergluing the windows shut so the vehicle can't easily be aired out.

I don't really know, but I would think that it would be advisible to wait a week or two so that the idiots won't put two and two together. I would also think it better to do this away from the house if possible.

Brake fluid on the car-paint!!
LOVE that piss smell in the cars intake vents too.  But check this out...  There are 574 users reading this right now, post the address and even if 100 people send in a magazine subscrption... geeze, I would hate to be him, calling all of those people to cancel!  HA!!  What about a *67 call (or whatever blocks caller ID) to every food delivery joint in the area!!

Make them homemade cookies and fresh-squeezed lemonade. When they come over to enjoy the goodies, invite them to watch a nice movie like "Heidi". Politely ask them respect you and your property so that you can all get along.

It's the only way to deal with the f+ckers.... [:D]

You guys rule.  I think we're going to put in a call to a city housing inspector because we know the house will not pass an inspection.  Thanks for all your responses!