All friends throughout my life knew, they learned at one point or another. I've known I was autistic since I was 6 or 7, so the knowledge that I was autistic was an integral part of my identity/life from that moment forward. Any friends that I played with soon found out about my quirks and also my tantrums, so anyone who had dealings with me would soon learn 'Look, it's because I'm autistic that it's like this-and-that'. Now that I'm mature, I don't have friends per se, but my one close friend -not autistic- I told her by-the-by. I usually do that, at some point where it becomes relevant, I'll just go "Oh, did I mention I'm autistic?" Usually when the subject of conversation turns to stuff directly pertaining to social relations, to childhood experiences, or especially when the topic is autism itself. So yeah, people who hang out with me long enough, will find out at some point ranging from immediately at the beginning to 2 months into the relationship.
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clarity of thought before rashness of action