We've all heard it. I even got it in Norwegian recently. It's number 1 on the list of responses to the statement "I'm a mathematician.". Does anyone have any good comebacks? What other responses have you heard?
Standard community wiki rules (not that anyone seems to take any notice of them): one answer per post please. Also, no snide comebacks, please - keep it nice. Extra kudos for answers that would actually educate the other person.