problematic-just-because:

Sherlock has to bring Mycroft and Molly together to help plot his fake-suicide, and, of course, it’s like the collision of two fiery, sass-suns, but they both (ironically) see the other as this poor, depressed, lonely soul.
So as they’re wrapping up a Killing Sherlock meeting one night (Sherlock tried to protest the name, but he really has no say in the situation), one or the other decides that “Okay, I’m taking you out tonight,” and the other’s response is just a shocked, “YOU are taking ME out?!” And in that instant they become best friends and go out and try to pick up guys together and they text constantly and they have cat-play dates every other week.

Necessary Addition Concerning Cats:
When Mycroft finds out about Toby, he of course conducts the (literally required) ‘Crazy Old Cat Woman’ taunting. Then they go to Mycroft’s a week later and it turns out he has TWO cats. Needless to say, he never heard the end of it.

problematic-just-because:

Sherlock and John once left the country for a case- completely unannounced. As revenge for their recklessness Mycroft and Mary took over the detective business for a time. They were extremely well received because of course they were faster, more polite, and in line with the law. When John and Sherlock got back they had absolutely no clients and had to negotiate with Mycroft and Mary to get them to stop- negotiating of course included several humiliating apologies.

-They do this all the time.

-Mary makes Mycroft wear the deerstalker.

-Mycroft ~negotiates~ with Greg to get more cases.

-There’s a scoreboard in Baker Street for most cases completed in a week. All spots belong to Mycroft and Mary.