I know a guy who did that with a motorcycle and forgot to go back and tighten it. When that plug vibrated out, and it did it in a hurry going down the road, well let's just say things got interesting. I think he shit himself.
It's one thing when someone makes a mistake, and/or is forgetful when working on something, but what about this?
There's a guy I used to work with who drove a '69 Fury III 4-door sedan. He bragged about having a "fully chromed engine". Well, I guess if rattle-can chrome counts, then yes, he had a fully-chromed engine. Same guy went to install an aftermarket pop-up sunroof in that same car. Problem is, he cut the hole in the roof the same size as the outer trim. He had to drive around with a hole in the roof until he could locate a bigger sunroof to install. And finally, he was heard telling another coworker that he only buys his timing chains from the wrecking yard, because they're so much easier to install than the new ones from the store. Said it was worth it, even though he had to change the chain out about every year, to year and a half.
Some people's kids...