"Son, not everybody likes firearms. In fact, some adults don't want to have anything to do with them. You need to ask your parents what they think about firearms. If they don't like firearms then don't make them angry by asking to learn about shooting."
Never let a good thing, like asking permission, go unpunished. Too bad for the kid. That sort of behavior is unforgivable.
Look at this as a learning experience. Don't dwell on it too long. Sometimes poop happens regardless of the goodness of the intent.