Rating 12+ (depending on your imagination)
Spoilers: Minor for Scandal in Belgravia. Inspired by a comment by Shoudboverthis.
"You're pick-pocketing Lestrade's phone now?" John said, when Sherlock gleefully produced it.
"He was being particularly irritating today."
"Well, maybe he's in a bad mood because his marriage has recently broken down, which would piss off anybody. And especially leave him feeling pissed-off with the person who's been providing a tactless running commentary on the disintegration of said marriage for months."
"But do you know why I pick-pocketed his phone now?"
"Because you're a git. A very clever git, but still a git." That was an easy deduction.
"To see what he's been saying to Mycroft."
John's jaw dropped. "Do I want to know?"
"Mycroft's been lusting after Lestrade for years. Now he's available, he'll try and make a move. I want to hear him being rebuffed." Sherlock opened the phone and started scrolling through the folders on it. Then his jaw dropped.
"I take it, then, Mycroft hasn't been rebuffed," John said eventually.
"There are photos of them together doing... things. I think my brain may be broken."
"Let's have a look," said John, and Sherlock handed the phone over. "Oh, that's not so bad, as long as you're careful. Done that sort of thing myself, actually."
"You have?" Sherlock demanded, in horror.
"Yeah, though you'd obviously have to be even more careful if you did it with another bloke."