A keybanger is to coast along in an manual carby'd car with the engine off pumping the go pedal 3-4 times then with the car in gear droppingthe clutch causing the car to 'roll start' causing a great bang to show you mates you need a new muffler.
turning off ignition (usually in a stickshift), let it turn engine for a second or two, and turning it back on for a cherrybomb-like report! Works best when you're beside a pedestrian!
Expect to replace your muffler...