Flames out the tail pipe:
Run rich and put a spark plug on a switch about 5" back from the end of the pipe. You cant use a cat as it will burn up any extra gas. Anyways, you gotta give the spark plug some major power, your choice how, but then all you do is start up you car, and flick the switch for a 3 to 4 foot flame of death.
Just so you know, i dont condone this, so attempt at you own risk.