<human>: Can you succinctly summarize the text in 1-3 sentences?

OK... weird and off the wall. My husband is 48, and we're watching our 5-year-old granddaughter overnight. They're goofing around and he moons her. I was horrified and like lightning, I grabbed her head and sort of turned it to the side and diffused the situation. I explained it like he bent over and his pants fell down a little, but she pretty much saw him do it.

He honestly is absolutely clueless about how inappropriate it is. Where he grew up, mooning is a perfectly acceptable prank to play on someone no matter what their age or gender. He related an incident where a relative mooned him at a party when he was a kid, and of course I brought up the fact that it was an uncle, he was a boy, etc.

I explained how totally inappropriate it is considering their ages and genders, and I guess he understands, but still thinks I made way too big a deal out of it.  I told him I would get some other opinions.
<bot>: My husband mooned our granddaughter and doesn't see what's wrong with it as everyone does that where he grew up.  How to impress upon him how inappropriate that is?