| I am making no bones about ripping this idea off. While reading What to do with that insane amount of shaving cream you have just lying around I was inspired.
What you need:
- about 20 cans of compressed insulation foam (the kind with a tube on the outside of the can for getting into small spaces)
- Pliers
- Tin snips
- plenty of liquid nitrogen
The procedure is the same as previously listed. Soak the cans in the nitrogen, freezing the foam, cut the can away and insert the frozen can-shaped brick of compressed foam into a car. Allow to thaw. The twist is this: The foam turns to a solid after a while, making it impossible to clean up. If you can not get access to the person's car and are willing to risk capture wait until they leave their window open a bit. Then just insert the tube in the window and empty the can into the car. This method will probably take many hours of standing next to the car red handed.
weasello says "liquid nitrogen will create an explosively volatile cannister. I recommend liquid oxygen for your desired results."
Good safty tip, thanks weasello, but that explosive canister thing sounds kinda fun. | 
