Underwear Party

My son says to me, "Mom, is it okay if I have a bunch of people over on Saturday?" I said, "How many?" He said, "A lot. It's Jacob's party, really, but he wants to hold it over here." I said, "But why does he not hold the party at his house? I don't really want loads of people over here I don't know. And who's going to watch them? I don't want to watch them!" I was exasperated. He said, "Yeah, I know. But Jacob wants to hold an underwear party, and his mom won't put up with that stuff."
"Underwear party?" I said. "What's an underwear party?"
"It's a party where everyone wears only their underwear. And anyhow, it's not like we aren't all friends."
"But... I don't know if I want to hold that at my house. How do I know they won't be doing... stuff? Argh! I can't deal!"
"Mom, it's no big deal. Like, girls wear the same type of clothes at a beach. Swimming suits. And anyhow, we're friends. It'd be just wrong if anyone tried to do something."
"But why does it have to be an underwear party? Why can't it be a regular party, for example?"
"Because - who has ever had an underwear party? That's right, no one."
"Well, hmm. That's an interesting concept. I'll think about it." And I'm still thinking about it.