Cases: NO TIME FOR REAL CASES. THERE'S PORN ON THE HORIZON. (Either story begins just after a case, or incorporates a few legit-sounding details.)
Anderson: Not usually in story but inevitably mentioned with appropriate scorn.
Mycroft: Usually either very for or very against Johnlock. Either way he's kinkily watching the CCTV.
Tea: Everyone drinks at least half their body weight in tea during the course of a story. Even drabbles. You see that 800-word story? 400 of those words deal with making tea.
Milk: Getting the milk is a thing. It's practically a euphemism at this point. If Sherlock gets the milk, he's DTF. Or apologizing, and then offering his body as an extra form of apologetic-ness.
Mrs. Hudson: Ships Johnlock like a beast. Hell, she usually has some kind of Johnlockfucking-sense. She just KNOWS when they're hooking up and is determined to facilitate this/make it kind of embarrassing for them in a cute way.
Mummy Holmes: For not actually being in the show, she's surprisingly mentioned a lot. She's everything from a horrid bitch to actually a really loving rich lady who somehow just has these two weirdo sons.
Moran: Ditto, kind of. Moran is sometimes a woman, sometimes a man, sometimes seduces Moriarty/John/Sherlock/all of the above. Also somehow capable of holding 7 laser pointers I mean snipers in TGG.
Jumpers: JOHN WEARS JUMPERS ALL THE DAYS AND SHERLOCK SECRETLY LIKES IT.
Boredom: The best way to cure Sherlock's boredom to sex him vigorously. Or somehow get him hooked on James Bond and/or Doctor Who.
Sexytiems: This is the fun part. There is so much beautiful variation here. John is everything from secretly gay, to comfortably bisexual, to not even really wanting to fuck Sherlock but kind of wanting to anyway. Likewise, Sherlock is everything from purely virginal, to wholeheartedly asexual, to secretly shagging half of London for a case. Their sex ranges from WE ARE GODS OF LOVEMAKING to it goes where?
Common Situations: Being outed at crime scenes, very thorough medical investigations, post-case-compulsion-to-fuck, the Scotland Yard has a betting pool, heartfelt realizations during kidnapping, gratuitous casual high-functioning sociopath nudity.
Violin: Totally a euphemism. He took dat bow in his hand like some kind of musical god slut and handled it with sexual precision.
AUs: Dude, I don't even understand this crazy shit. There's wings and cats and Greek alphabet letters thrown all over the place.
Genderswap: Love it, but it's really funny because we never know what to call Sherlock other than Sherlock. Sherlock...ina? Sherlockette? Dafuq.
Avengers: They show up a lot, somehow. I think it's because we're all from tumblr and Hiddles is love.
Conclusion: I fucking love this fandom never change.