Thanks for the replies, everyone!

Uncle Al, I prefer the "That's for me and my wife to know" reply best, I think Neither of us are wanting to give anyone any ideas (and I certainly don't want to know if I'm the sort who'll end up throwing a punch if I see someone lifting his kilt). But yes, I've told him to definitely stay on his toes as far as witty replies go and to be prepared for questions, and I'm sure he'll have plenty to say to anyone who attempts to take things too far.

(we were amused at the guy who asked the Question -- he obviously wasn't prepared to actually get an answer and I think realized immediately that he really shouldn't have asked)