The funniest part of this conversation was that it wasn't said in a "smarty pants" tone. My son was sincerely asking.
Me: "How was your home school class today honey?"
Me: "What did you do?"
Mark: "...(pause)...Um...Mom...can I say 'None of your business?' "
Me: "No, that would be very rude."
Mark: "Oh, well it's a good thing I didn't say it then, eh Mom?"