John and Sherlock get together. They are in love, but Sherlock won't let them get really intimate with each other. John thinks that sex just isn't Sherlock's thing, as he's always suspected, and maybe he's quite right, but there's more to it. One day he learns that Sherlock is intersex. John assures him that it's alright and, contrary to Sherlock's fears, John absolutely won't be disgusted by him.

I would love John to play with Sherlock's genitalia and arse with his mouth and fingers, lavish his body with affection, inspect it thoroughly (give Sherlock an orgasm or two in the process), and only then penetrate him.