Lose your temper. Back in the days before circuit breakers, a house's electrical system was regulated by a fuse box. Individual fuses connected to separate lines throughout the house were inserted into the box. When a circuit became overloaded, a thin metal strip in the fuse melted, breaking the circuit to prevent an overload and a possible fire. You'd then replace the fuse after disconnecting whatever appliance might have caused the overload. Someone who because very angry was said to blow a fuse, which doesn't make sense because a fuse was meant to defuse, so to speak, the situation. But no one ever said that idioms must be rational. Similar expressions that make more sense are “blow your stack,” which came from the era of steam engines that would explode if the steam wasn't allowed to explode, and “have a meltdown,” as in a nuclear reactor gone wild.