It was a word he despised.
Sherlock knew it was childish, stupid even, to hate something as small and insignificant as a simple word. And he was never one to concern himself with silly things like that. But the fact remained: he absolutely HATED this particular word. He always had.
Mycroft hadn't ever liked the term himself, but much to Sherlock's puzzlement, he had come to accept it. Embrace it, even. He gave to charities and spent a good deal of his time talking to children about the hated word. "It isn't something to be ashamed of, Sherlock", Mycroft had told him once. Sherlock pretended to not hear him.
He had almost completely cleared the word from his mind, forgotten it existed entirely, when he overheard John say it to Lestrade, and that old familiar rush of emotions caught in his throat.
And suddenly, Sherlock was five years old again, sitting disinterestedly next to mother in the antiseptic doctor's office, staring into space. Mycroft is more engaged, being older, but he is just as uninterested. The doctor, he can quite clearly remember, was a rotund man of fifty-something, with grey hair and glasses. His voice is soft, kind, but heavy with bad news. "I'm afraid there's not much we can do about it, Mrs. Holmes. Therapy, and a good school would work wonders for them both, but moreso for Sherlock." He looks up when he hears his name, catching the silent tears that fall from mother's eyes. He squints, trying to figure out why she's crying. "But children like them can be very productive members of society. It's not like it was. They'll both have good lives if they get the help they need."
Twelve now, and he's sitting alone in a field, studying a dead squirrel he'd found after school had let out. He finds the internal organs beautiful in the way they work and connect to each other. The other children tease him, and it's the first time someone ever calls him a freak. It doesn't register, and Sherlock doesn't understand why mother gets upset and hugs him. He doesn't want to be touched.
Mycroft turns 17 in his flashback now, already in college and he wants to move out of the house. Mother begs him to stay where she can keep an eye on him, and Mycroft erupts into a fit like he hasn't had in years. "You treat us like we're broken! There's nothing wrong with us!"
Sherlock doesn't eat for days after Mycroft left, refusing to talk or to do very much of anything but practice the violin. He had broken much of his things in a rage he couldn't control, and he wasn't sure but he might've thrown something at mother. Guilt didn't last long. She deserved it, making Mycroft leave. He hears the word again, and now the violin is shattered on the floor.
Freak. Everyone calls him that. Everyone thinks it. And it never bothered Sherlock because that word was just as meaningless as all the rest of them, a simple, dull, meaningless opinion from simple, dull people.
But this wasn't just anyone. And it wasn't just any word.
Snapping back to reality, he put on his best blank face to mask how badly John had hurt him. After what he had said and done to John the night before, perhaps he had earned it.
But late that night, when he knew John was asleep, Sherlock allows himself to cry a little.
Lestrade: I suppose he likes having the same faces back together. It appeals to his… his…