Steven Moffat had some words for Vulture on Sherlock's best man speech in “The Sign of Three,” his need to write the scene since he was a child, and Sherlock's determination to convince the world that he's a sociopath. It's an encouraging breakdown that speaks well for the character and his particular set of flaws. Take a gander...
Though Moffat hasn't ever been particularly complimentary of fan fiction, his desire to write Sherlock's best man speech basically confirms that he's in the same boat as most fans:
“I remember being a 12-year-old kid thinking, Oh, why didn’t we see Sherlock be the best man? Please, can we see that? That would be the best story in the whole world, and I don’t care if there’s a crime in it or not, because it must have been the best and worst speech of all time!”
So 12-year-old Steven Moffat wanted to write some serious Holmes fanfic—he didn't even care if it was mystery-free. And when he finally got to do it, his childhood plan came to fruition, one where he decided that Sherlock would begin the speech by acting as awful as possible because, “he’d sit there and think, Everyone’s gonna think I’m gonna make a right cock-up of this. Everyone thinks I’m going to screw it up. So, I’m going to make them think that, and then of course I’m going to say something lovely.”
Sherlock's involvement in the wedding planning process was also addressed by the show's production designer, Arwel Jones. He pointed out the little touches throughout the detective's flat meant to intimate how involved he was in putting the wedding together due to his “control freak” nature. Which is not only coo-inducing, but economical; just think how much money the Watson's saved by not needing a professional wedding planner.
But back to that speech: According to Moffat, Sherlock's seeming insults toward everyone at the wedding—John included—is just a bunch of BS before getting to the good stuff:
“He always is [bullshitting]. He doesn’t think that at all. He doesn’t think any of those things, but he wants to think that he does, just as he wants to think he’s a high-functioning sociopath. He’s not a sociopath, nor is he high-functioning. He’d really like to be a sociopath. But he’s so fucking not. The wonderful drama of Sherlock Holmes is that he’s aspiring to this extraordinary standard. He is at root an absolutely ordinary man with a very, very big brain. He’s repressed his emotions, his passions, his desires, in order to make his brain work better — in itself, a very emotional decision, and it does suggest that he must be very emotional if he thinks emotions get in the way. I just think Sherlock Holmes must be bursting!”
Which answers a lot of long-standing fandom questions in regard to Sherlock's true stance on emotion, his self-labelled sociopathy, and his wants versus his reality. Sherlock Holmes wants to be emotionless, he wants to be a sociopath, because he is—at his core—a deeply emotional person. (Who has been taught by his older brother that emotions are terrible and that he's the stupid for having them.)
Now we are free to ponder the implications of that to our heart's content.