Self-destructing garage door opener
I once lived in a house which had an interesting arrangement for its garage door opener. For whatever reason, it had an outlet on the ceiling for the opener which was switched. In every other place where I've lived, that ceiling outlet was nothing special, but this house was strange. It had a third light switch in the garage, right next to the ones for the actual interior garage light and the lights outside.
Let's say you went out to the garage at night and turned on the light with switch #1. You had to make sure you only turned off that same switch as you went back into the house or you'd take out the garage door opener.
To make matters even more interesting, a burglar alarm had been installed in that house, and the installer chose the garage roof outlet as the location for the system's transformer brick (wall wart). Apparently they do that because "it stays out of the way and it's always on". Yeah well, this house played by its own rules.
Taking this to its logical evil extreme, you could break into the unmonitored garage and turn off power to the alarm, then wait a few hours for it to lose battery power. Then you could just open the door and walk around stealing stuff. This never happened, but it was a plausible scenario for someone with too much knowledge about the place (like a former resident).
The fun didn't end there. Even with the burglar alarm system fixed up and relocated, that outlet was still switched. We figured it would make a handy security feature, since we could take a car out, bring the garage door down, then go in through the house and turn it off. That way, people driving around with those brute-force garage door hax0r devices would be thwarted.
That was all well and good when the switch was off, but there was a catch when it was time to turn things back on.
You see, the garage door controller forgot it was already "down".
So, the first time someone pushed that button, it would try its very best to drive that sucker further into the ground. Of course, since the ground was actually solid and so was the door, all of that energy escaped into the big metal thing which actually rotates, and it started "skipping" in and out of the groove at high speed.
It was incredibly loud, and to be honest, it was rather frightening the first couple of times it happened to me. Imagine a jackhammer suddenly starting up right next to you and you'll have some idea of how loud it was.
Of course, turning the power off just started the cycle over, so finally someone figured out that we had to power it up, push the button and let it make the awful noise, and then immediately push the button again to make it stop. Then it would go up on the next button press.
It should come as no surprise that this thing eventually died a particularly nasty death. I guess a number of power outages (from the switch or otherwise) set up this situation a few times, and it eventually destroyed itself.
The replacement system wasn't cheap, but it had both the newer sort of remotes which are harder to spoof and a proper set of "up" and "down" limit switches. This one wouldn't freak out when you rebooted it with the door down, in other words, and there was no longer any reason to turn it off for the sake of "security".
The one thing which never went away was that switch. We just put some tape over it to hold it in "on" and left it at that.
As long as I'm talking about garage power outlets, let me add another fun one. If you've lived in certain mountain regions and have mysteriously lost power to your floor-level garage outlets, I bet you tripped a ground fault interrupter in one of your bathrooms. For some reason, they really like to rig things that way in that part of the world. I know a few people who lost all of the food in their deep freezer that way, and it was not a pleasant thing to clean up.