Take a bunch of confettie (well you get the idea) I can't spell it. Stick it in the air vents of someones car while they aren't around. Make sure you put a bunch of it in every vent. Now take some fart spray and spray it all over the vents. Now, the next time the person that owns the car gets in and turns on the vents, Confettie will fly everywhere and the nasty smell of fart spray will shoot out of them. It's really hillarious. Try it.