Well first off, I would notify a parent and let them know what your brother did.
Second off, don't let your brother hit you with things.
And third, if he's being rude, you have the right to ignore him.
Protection for offensive speech—even flag burning—is the bedrock of the First Amendment, because ideas we all share need no protection. The First Amendment protects unpopular opinions so that speakers and listeners have the freedom to decide for themselves what speech is worthwhile and what speech should be rejected.