Arlen...

At that point (when she got condescending and rude) I would have blown off a little steam with 1 of the following options:

1. (looking at her jacket or shirt side to side) "Hmm.... Sorry, I can't seem to find your TARTAN POLICE badge. Are you going to write me a ticket?"

2. "Well you MUST know what YOU'RE talking about. I'm not from Scotland and didn't pay top dollar for my kilt in someone else's tartan that I have nothing to do with. Yup... you MUST be right b/c you saw your brother in law wear a kilt once... if that doesn't make you a tartan expert, I don't know what would. You should offer your services to the Scottish Tartans Authority with that eagle eye of yours."