Sherlock's first time wasn't. But he'd deleted the many first times before that. And no one was counting. Except Mycroft of course.
The first first time had been at school. It hadn't been entirely consensual. But neither had Sherlock at any point asked his would-be lover to stop or said no. He had regarded it as a curious experiment. He repeated the curious experiment several times before drawing the conclusion that his data set was insufficient and deleting it all. James, the would-be lover, had been quite heartbroken about it, he'd been a sensitive, clever boy with stormy eyes who didn't understand how one day, just when he thought he was getting somewhere, he had been dumped. Forgotten and abandoned like a favourite toy a child had become bored with. James never really got over it.
The second first time had been at University. Vic was bigger and less intense than James. Not that Sherlock remembered in order to be able to do a comparison in any case. Vic was a bit like an affectionate Labrador that fawned all over Sherlock, told him he was beautiful and wanted sex in odd places. It went on for some time before, on his third heroin high, Sherlock deleted the lot. The following morning at breakfast Sherlock announced to the college that Vic had been shagging the night before. Vic was too much of a gentleman, and rather too confused to divulge that it had actually been Sherlock he had been shagging.
The third first time Sherlock had not had to delete. He never remembered it to begin with. Occasionally flashes of a dirty mattress and the smell of sweat and rat piss flickered across his thoughts and was dismissed. High. Veins screaming despite the drugs running through them, crying out for more. Used needles crunching on the floor and the play-doh face of someone he didn't know who was just as high as he was looming large above him. It was shame he couldn't remember this one in some ways. The drugs stripped all the veneer away. All the lies and pretence until Sherlock was naked on the filthy mattress, emaciated and dying but at the same time more alive than he had ever been before or since.
The fourth first time probably counted as a first first time as well, as it was with a woman. The Woman. As she had dominated him and slapped him and stripped him and drugged him. And then she'd had him. And he had been unable to do anything. His intellect shredded and useless, discarded along with his boxer shorts in a crumpled heap. Clever didn't matter. Reason didn't matter. All that mattered was him and her. For that moment. Afterwards he had been so horrified, so afraid of those feelings she had seen dancing through him that he deleted it all. Almost all. But before he did, he'd told Mycroft. Mycroft already knew, but that didn't matter. What mattered was that Mycroft would remember, so he didn't have to. He knew she was always The Woman. But he couldn't remember why.
And then of course was the first time he did remember. Which was ironic as it was the only first time that had never actually happened. But the human brain is a powerful thing. And the brain of a genius more powerful still. So powerful it could change reality.
The first time with John Watson. When finally they slipped into the cool linen of that single bed. The landlord had apologised he didn't have a double room. It didn't matter. It was just as sweet. John offering comfort. Sherlock taking it. The slow movements becoming rapid, the ghosts of John's touch becoming solid and real. Sherlock surrendered his fictional virginity. Gladly. Willingly. Feeling his release. Feeling the pieces of his life's puzzle slotting into place. It all made sense.
The first time with John was the only time Mycroft didn't seem to know about. Perhaps he had deleted accidently? But Sherlock would always remember.