Everybody loves a prank. Particularly when it relates to flatulence, and suggesting a causal relationship between the yanking of a digit (not a euphemism) and the sound of a car back firing.
What you need to do however is let the world to expect some serious fireworks. Anybody dare pull your chain and shits (literally) about to get real. Think bottom burp par excellence, singed pant fabric, and a follow-through with a blast radius of metres.
Wear this Pull My Finger t-shirt and people have been suitably warned. You’re then free to focus on explosive material – from beans to a good curry – that’s going to create some serious collateral damage. Magnitude 7.4 on the Richter Scale? Nod arf!