smores
Creepy-Ass Cracker
I'd vote for the engage politely approach. Makes them look like more of a fool, and actually put those dirty looks into words.
My plan if I'm ever approached buying guns/ammo etc. Is to ask them if they own a digital camera. When they say yes, I'll ask them if they are into creating child pornography. I think they be offended at the thought, and it may make them think that that's exactly what they've done to me with their assumptions.
Note: I had to think of this plan in advance, because otherwise I'd bust out something creative like "oh yeah! You are! " -- then I'd be pissed for a week afterwards..
I was at Wal-Mart in Germantown, buying 9mm and .22 LR. Cashier asked, "are these for a handgun?" I said "No, actually they're for a full-auto UZI and a bolt action .22". I just got a blank stare for a few seconds until she punched in "1950" for my birth year on the register. I'm 24 lol.