I don't mean to be rudeโ" he began, in a tone that threatened rudeness in every syllable. "Yet, sadly, accidental rudeness occurs alarmingly often," Dumbledore finished the sentence gravely.
J. K. RowlingDo you remember me telling you we are practicing non-verbal spells, Potter?" "Yes," said Harry stiffly. "Yes, sir." "There's no need to call me "sir" Professor." The words had escaped him before he knew what he was saying.
J. K. Rowling