[John visibly bristles at the use of the slur. It's been so long since he's heard Sherlock use the word, and it's jarring to hear it again. Disappointing and, yes, hurtful too.]

You do not get to use that word again just because you've got two memories mixed up in your head. I don't care what the other bit thinks of the situation, but I know part of you knows damn well what that word reminds me of. You haven't used it in a long time, and I'm not about to just let you start up with it again.

Understand?