The first time he heard the insult, he was four. A boy in his class called him that after he read a book during what was supposed to be nap time. The teacher scolded the boy and gave Sherlock a gold star for trying to read "Peter Pan", a book most people don't read until they actually start school. What she didn't know was that he had actually read the book ten times before, and already knew more words than she would ever use in her lifetime.
The second time he heard it was when he was six, and he heard it multiple times that day. He sat alone, in the school yard, while his classmates threw massive seeds at the walls, or kicked around a football. Sherlock kept reading, until the biggest boy grabbed his book and hit him with it. That was Sherlock's last day in public school.
Over the course of his time in private school and university, he heard the insult precisely 3,822 times, but he doesn't keep count anymore, he deleted information that to store facts about the rachis of feathers from a peacock.
Sally Donovan liked the insult. She used it often enough, especially when her supervisor isn't around. Anderson too, but 68% less that Donovan.
The media was more creative with it's insults, but the same word still popped up, now and again.
John never used the insult, and for that, Sherlock was grateful. John yelled at him sometimes, was angry at him sometimes, but never used the term that echoed throughout Sherlock's life. John was the only person who made him feel like he didn't deserve to be called it. Didn't deserve to be a freak.