Creator In-Joke: A brief shot of an inn called 'The Punch Bowl' is visible. Guy Ritchie owns a pub called The Punch Bowl in Mayfair.
Credits Gag: There are a couple, mostly in the juxtaposition of assorted credits with images from the film. The best of these is that the Costume Designer's credit appears with an image of the naked Holmes tied to a bed.
Deleted Scene: So, Irene never got around to trying to stab Holmes with a hair pin or kneeing him in the... meerschaum, eh?
Watson, due to being taller, thinner, younger and more Jude Law than some previous portrayals, quickly became known as Hotson.
Stephen Fry's version of Mycroft Holmes quickly took on the nickname "Frycroft".
Fandom Nod: In the extended preview (aired during the Monk series finale), there's yet another clip of the Holmes-Watson Vitriolic Best Buds routine, then a cut to Adler going "They've been flirting like this for hours." To the general public, a funny joke. To those aware of the Holmes/Watson-shipping fanbase, bloody hilarious. As it happened, this seems to have been a deleted scene referring to Watson's bickering with a boat captain.
Jossed: Rumors circulated that Brad Pitt was in the running to play Moriarty in the second film. These were quickly denied, saying Pitt had never been considered.
The Other Darrin: Jared Harris as Moriarty, in a way. Since, technically, he appeared always in shadow in the first movie and was played by Ed Tolputt in an uncredited role. Jared Harris redubbed Tolputt's lines to give it continuity with the second film in subsequent TV airings of the first film.
Real Life Writes the Plot: In the original stories, Holmes is trained in Baritsu. In the film it's Wing-Chun Kung Fu - because Robert Downey Jr practices that in real life.
Referenced by...: Canadian figure skater Stephen Gogolev performed to the Sherlock Holmes soundtrack for his long program during the 2018-2019 competitive season.
Trolling Creator: Rachel McAdams tried to trick the wardrobe department by eating a large breakfast in the morning or pushing out her stomach during fitting - in the hopes of her corset not being tied so tight. They eventually caught on to her ruse.
Sienna Miller was in talks to star in the film, possibly as Mary. But when Jude Law was cast as Watson, this was quietly dropped - due to the couple's very public break-up when Law had an affair with their nanny.
Sam Worthington and Colin Farrell were in talks to play Watson before Jude Law was cast.