My most common is "Is there some Scottish thing on?" (usually not that I'm aware of), followed by "What tartan is that" (one form of Gordon or another), "Why is there a knife in your sock?" (technically it's not called a sock. Or a knife for that matter. I use it to slaughter Haggis), then "Do you play the pipes?" (no, although I can raise a single noise, midway between breaking wind & a cat being plucked. One particularly thick person got the reply, "No, do you play the banjo?" but they didn't get it).