The other side of that is, how is it appropriate to ask anyone what they're wearing under their clothing?

I mean, it's one thing to be interested in the kilt and if you're wanting to get one, to find out HOW to wear it. It's quite another to blurt out loud to a stranger "hey! What are you wearing under that thing?"

I think Thunderbolt's simple question back is a polite way of saying "that's really an inappropriate thing to ask". Especially if done in a non-venomous, surprised way.

Sure, stay calm. Be polite. But you still have the right to educate people by letting them know that really isn't proper to go around asking or or lifting someone's clothing.

To me, that doesn't make the kilt wearer out to be a meanie to protect their rights for privacy. If the person asking that thinks that, they're the one with the issue.