pfff, root, back in my day we hacked a vending machine with a lighter and got free coke.

No idea who discovered it, but the machine back at my school had an infrared interface for servicing, and you could trigger an interrupt with the flash of the flintstone of a lighter. Because it's just some 90s microcontroller, it would simply reset after failing to receive a valid command and forget what it was doing previously.

All you had to do was order a coke, and right when it drops out, before it subtracts the amount, you flash the lighter in front of the IR port like a magician, say the magic words and bam - free coke!