Having never been formally diagnosed, it would seem wrong for me to tell friends and colleagues that I have AS, despite the level of certainty in my mind that I do. At this time, I cannot ever envisage myself seeking such a diagnosis; but even if I did, I would only tell closest friends.
My fear is that people would treat me differently than they had done before, upon finding out. At the moment they gently poke fun at my quirkiness, and I have no problem at all with that, in fact I quite enjoy it. I can't recall being poked fun at, even maliciously, ever provoking a negative emotional response in me. (My hypothesis is that I was told the Sticks and Stones verse* in my formative years and took absolutely it to heart.) I find that allowing oneself being gently poked fun at helps cement the bond between the both parties and for this reason such ribbing has become the social norm. However, it is a social taboo to poke fun at any facts about a person that have been given a 'label' (and for quite laudable reasons). Informing people that my eccentricities have the 'label' Asperger's Syndrome would stop them from joking about them. This response would probably be so automatic to them that my telling them it is unnecessary would not change it.
As for my family, I have never voiced my suspicions to them. I think the most probable response would be not to take me seriously. Were I to be diagnosed, I would feel compelled to tell them. My fear here is that they would feel some sense of failure on their part for having never themselves suspected anything. At the moment stories about unusual things I have done or said are told by them with the unconditional parental pride and I don't want to take that away from them.
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*Just in case this isn't international, it goes: "Sticks and stones may break my bones, but names will never hurt me."