"So," said John. "The big question."
"Mm-hm," Sherlock said, turning to face him.
"The best man," said John. He folded his hands on the table.
"The best man?" Sherlock repeated.
"What do you think?" John said.
"Billy Kincaid," said Sherlock immediately. "The Camden garroter. Best man I ever knew. Vast contributions to charity, never disclosed." John frowned. " Personally managed to save three hospitals from closure and ran the best and safest children's homes in north England.
John tiredly rubbed his fingers over his eyes as Sherlock grimaced momentarily, lost in thought. "Yes, every now and again there'd be some garrottings, but stacking up the lives saved against the garrottings, on balance I'd say-"
"For my wedding!" John interrupted. "For me. I need a best man."
"Oh, right," said Sherlock.
"Oh, Mike Stamford, I see. Well, he's nice, um, though I'm not sure how well he'd cope with all-" started Sherlock.
"No, Mike's great, but he's not my best friend," John interrupted. Sherlock looked thoughtfully at him, trying to think of another friend to suggest.
"Look, Sherlock, this is the biggest and most important day of my life," John said.
"Well ..." said Sherlock dubiously, pulling a face.
"No, it is! It is, and I want to be up there with the two people that I love and care about most in the world," said John, wishing he would understand.
"Yes." Sherlock waited for John to tell him who they were.
"So, Mary Morstan, and..."
"Yes?" said Sherlock again.
"And... you."
Sherlock stared at John, blinking rapidly for a moment. John stared back.
Sherlock didn't move, didn't so much as blink after the initial few. It was as though he had frozen in time.
"That's getting a bit scary now," said John awkwardly after a minutes or two.
Sherlock blinked once more, then spoke.
"So, in fact... you - you mean..."
"Yes," said John.
"I'm your... best..." John nodded.
"Man,"he said almost at the same time as Sherlock said "friend."
" Yeah, 'course you are. 'Course you're my best friend," said John, surprised.
Sherlock picked up his mug off the table and took a sip.
"How was that?" John asked him, disgusted.
"Surprisingly okay," said Sherlock. The eyeball he had dropped into it before floated to the surface.
The first time that John called Sherlock his best friend, Sherlock shut down for a moment. He literally went into a momentary shock. Sherlock hadn't been in shock since he was a child and had broken his arm so badly the bone poked out of his skin. But this was far worse than that.
Sherlock never expected to be anyone's friend. Being John's was more than he had ever hoped for. He knew perfectly well why he hadn't had friends and he had long ago resigned himself to he that fact. So when John called sherlock his best friend the first time, an honor bestowed only on the closest of acquaintances, he almost didn't believe it.
After a moment, he woke up again, so to speak. The thrill that ran through him of shock and surprise and of absolute amazement was beyond good. It was sublime.
After John recognized that, Sherlock was certain to put it in his speech. He almost didn't say it when he got to that part; what if John had been joking? What if he meant spatially? What if John changed his mind?
When he did get to that part, and said it, he glanced at John just to make sure that he reacted correctly. John nodded and Sherlock was exultant again. It was true.
But he couldn't bring himself to say it after that. He couldn't repeat it. Perhaps he had misread John's reaction. Perhaps John's best friend, now that he was married, was his wife. It seemed too unlikely to Sherlock that he of all people could be anyone's best friend, much less John Watson's. So he didn't say it at all, didn't even permit himself to think it, until a month after the wedding. Even then, it was only because of Mary.
When John found out about Mary's betrayal, he was reasonably certain that he would not call her his best friend at that point. He hadn't talked to any of his friends but Sherlock in a month. By all factors, Sherlock had to be John's best friend by default. So he tried it again, just to see if it would work.
"...and your best friend is a sociopath who solves crimes as an alternative to getting high! That's me, by the way. Hello!"
To his relief, John didn't even consider negating it. The high he felt just at that moment was better than any solution or drug he had tried before. Sherlock Holmes was someone's best friend - was John Watson's best friend! He hated having to move on so quickly from that, but bigger things were happening just at that moment.
It was okay, though. He was John Watson's best friend.