I'm sure that you'll regain your composure and offer them a very polite refusal.

You might go on to mention that they would have plenty of time to order a kilt, belt and sporran from SWK before the holiday and that actually owning and wearing one's own kilt might help to broaden their horizons, enlighten them and POUND IT INTO THEIR SHAGGY HAIDS THAT THE KILT IS NOT A COSTUME!

Try not to get steamed...

...it is easier to be a wise man on a mountain top than it is to be a prophet in your own land.

Best

AA