The old switcheroo
Pilot fish recalls the days before ATX power supplies connected to the motherboard. Back then, all PC technicians eventually had to replace a power switch when replacing a power supply, and almost all managed to pop a circuit breaker at some point by connecting the switch leads incorrectly.
It happened to a tech whom fish worked with in a most unfortunate way. He laid the new switch down while reaching to turn on the power, and when it shorted, the switch welded itself to the inside of the metal case.
Tech wasn’t looking forward to explaining what happened to the client, but in the end, the fused switch was removed with a little effort, and with a new switch in place, the PC was fine.