The Hounds of Baskerville - S2-E2
Deliberate mistake: The army major wears a full beard. British Army personnel may not wear beards. (The beard is a nod to the original canon character on which he's based, John Barrymore, who is described in the book multiple times as being a "black-bearded man").
Chosen answer: That line of dialogue has never actually been spoken in any of the Sherlock episodes, during seasons 1-4. However, that line is written in someone's fan-fiction story online, where it's said by Sherlock and directed at Anderson.
Super Grover ★