I understand the question. It seems that ... even in some branches of my family ... the kids just want to play Yugi-oh! and fit in. They lack the experience of having seen the things that someone just a few years older has seen. This is an opportunity to educate a bit, no?

But I think that to say "I'm Scottish-American" would suffice.

If that is not your case, which is totally cool, I'm sure there are ways to explain that the garment is part of a unique heritage of a strong and proud people. It's like a police uniform, or gladiator gear. ^_^

You could also cite the fundamental differences between a typical skirt and a kilt. The foremost of which is the fact that kilts are wrapped onto you and pleated in a manner that is part of tradition.