That's enough power, right?

This one happened a while back but I was reminded when I saw the same nimrod buying plastic conduit and PVC plumbing fittings.

Last fall this guy comes in wanting to buy some parts to hook up a new electric dryer. He explains that the house used to have gas but that he was recently given a used electric dryer. Fine so far. I ask if he had a 220V line at all in the basement. No. What kind of feed did he have running into the circuit box? He didn't know and it wasn't a circuit breaker box but old Buss style fuses. He had two 20 amp fuses in the fuse box.
There's no way this house, which was probably a converted summer cottage, had enough service to provide power for an electric dryer. I tell him so as politely ask I can but by now he's gotten some spark of imagination and starts grabbing parts off the shelf. Just enough to do some damage.
His buddy, another salesman, and I spend the next ten minutes trying to convince him that he's not qualified to do this and that he's likely to kill himself, set the house on fire, or both. He agrees to call an electrician but I watch him grab some "How-To" pamphlets on his way out the door.

Every year, without fail

"Do you have an extension cord with two pointy ends on it?"

NO!

Every year some doofus lays out some elaborate Christmas light display and every year they discover, when it's all over, that they ran all the strings backwards and they're holding onto the female end and standing at the receptacle. Every year they come come in to the store asking for an extension cord with two male ends, and every year I need to explain that no, "they" don't make such a thing. Yes, we have the parts for you to make one yourself. No, it's a bad idea because a) it's against building code to use an unapproved device for such a purpose and b) if you have any kind of accident and need to file an insurance claim your insurance company can just turn around deny your claim for that very reason.

Nine times out of ten then give up, but that tenth guy is just too lazy to re-run his entire display or too cheap to buy a hundred foot cord to reach the end of his lights.