“Please, sir,” said Hermione, whose hand was still in the air, “the werewolf differs from the true wolf in several small ways. The snout of the werewolf -”
“That is the second time you have spoken out of turn, Miss Granger,” said Snape coolly. “Five more points from Gryffindor for being an insufferable know-it-all.”
Hermione went very red, put down her hand and stared at the floor with her eyes full of tears. It was a mark of how much the class loathed Snape that they were all glaring at him, because every one of them had called Hermione a know-it-all at least once, and Ron, who told Hermione she was a know-it-all at least twice a week, said loudly, “You asked us a question and she knows the answer! Why ask if you don’t want to be told?”
The class knew instantly he’d gone too far. Snape advanced on Ron slowly, and the room held its breath.
“Detention, Weasley,” Snape said silkily, his face very close to Ron’s. “And if I ever hear you criticise the way I teach a class again, you will be very sorry indeed.”
—Harry Potter and the Prisoner of Azkaban