MYCROFT: You’ve met him. How many friends do you imagine he has? I’m the closest thing to a friend that Sherlock Holmes is capable of having.

WATSON: And what’s that?

MYCROFT: An enemy.

WATSON: An enemy?

MYCROFT: In his mind, certainly. If you were to ask him, he’d probably say an arch-enemy. He does love to be dramatic.

WATSON: Well, thank God you’re above all that.

Steven Moffat (b. 1961) Scottish television writer, producer

Sherlock, 01×01 “A Study in Pink” (2010-07-25)
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(Source (Video); dialogue confirmed)