Hey, I was polite about it.
If that's your idea of polite, what's rude? OK, I don't wanna know the answer to that...
I said (I believe), "Excuse me for asking, but who the fuck are you?" I have witnesses. I used a measured, friendly tone, and I was smiling. We chatted about bunny rabbits and such. It was a pleasant moment, my shrink says I'm getting better at personal interaction.