Lestrade ends up getting thoroughly pissed while out with John on one of their pub nights (maybe it's after he finds out his wife is cheating / post-divorce going through / etc.) and gets super-tactile. John doesn't entirely object to the idea of kissing Lestrade, but he doesn't want to let it go too far and then have Lestrade be upset/embarrassed/angry the next day.

Except the next day, Lestrade isn't entirely sure what happened and whether he just dreamed it. Maybe Sherlock makes some embarrassing deductions? Or John and Lestrade end up having to have a really awkward conversation?

Would be fine with John/Lestrade or John/Sherlock/Lestrade or pretty much any combo you want to come up with :-)