I am a huge fan of Miss Manners. She expresses the spirit of etiquette so eloquently, compressing books of arcane rules into simple ideas. Today she nailed it again, expressing a core idea of etiquette:
It is not uncommon for rude people to act offended when their rudeness is not tolerated. Miss Manners assures you that this does not make it rude to refuse to tolerate rudeness, as long as this is not done with retaliatory rudeness.