Some smart ass lowlife once said something ignorant after he heard me saying the dreaded "please" and "thank you".
I courteously told him that just beause I had manners did not mean that I did not have the ability or the desire to ruin his day. I said, "Since I'M the one with manners here, I think I should ask whether you would like me to kick your ass now; or would it be more convenient for you if I scheduled it for tomorrow?
He ran out the door.