grammar police

Someone or a group of people who insist on correcting or criticizing others for errors in spelling, grammar, and syntax, especially to a pedantic or self-righteous degree. A: "What are you, the grammar police?" B: "Hardly. Everyone knows you shouldn't use 'ain't' in a formal paper." I don't mean to be the grammar police, but you shouldn't use a semicolon to introduce a list—that's the job of a colon. A: "It irritates me to no end when people use 'good' as an adverb." B: "Well, keep that to yourself, because no one likes a visit from the grammar police."