You're in a job interview, and the potential employer asks you a question that's not only rude but possibly illegal. Now what? What do you say?
How about ... nothing?
Silence is uncomfortable for many of us, and it's human nature to want to fill it with something. Why not give the person who created the discomfort a chance to do that? You don't have to scowl. A weak smile, wrapped in just a hint of wide-eyed wonder, can be as effective as it is disarming. You might inspire the person to rewind a bit, perhaps even apologize. If nothing else it'll buy you a little time, maybe keep you from responding with something you might regret.
"Learn to pause," I can almost hear the poet Doug King saying, "or nothing worthwhile will catch up to you."