John made Sherlock a cup of tea
Sherlock took the cup and kissed John
Sherlock (after the kiss): Thank you, I’ll find the way to pay you back.
John: Um, Sherlock…
John: You do realise you kissed me, don’t you?
John: And why did you do it?
Sherlock: John, I’m a high-functioning sociopath, I’m allowed to kiss anyone I want, and I don’t need any reason to do it. Although, you being nice and making me tea is already a good reason.
John: It’s not about tea, is it?
Sherlock: Oh, it’s so not about tea.
And that’s how you do it.