FARK.com: (1219854) Man convicted of rigging his car to spray chemicals from the trunk. Claims it was for de-icing the wheels: "I've found at night that if I cycle the ignition on my Harley, the flames out the pipes generally work well to repel any BMWs tailgating me.
If you're in a stick shift car, downshifting to slow down's fun with tailgater's too, cause they get really close, panic, mash the brakes. Or tap you, which startles them too.
Other fun things include filling the rear wiper tank with brake fluid and aiming it out back, to nail tailgating cars. paint remover, acetone, etc is useful here too, but brake fluid has the 'I didn't know where it went' factor helping it.
A friend of mine had a Jeep Grand (? It's a tiny shiatbox) Cherokee that was one better - the rear window tended to pop out really easy. That sure worked on tailgaters. Though you had to then stop, fetch the window, and punch it back in..."