It's really interesting to see/hear/interpret the range of responses from people. Some people aren't surprised by it at all. Others completely disagree with the diagnosis and will say something. And others will obviously disagree and not say anything. And some even responded in ways that don't make much sense at all. (One of my best, long-term friends responded with "well, you've always been a great friend to me!" when I texted him the diagnosis). And others will just not say anything and will avoid the conversation.
I'll say that the myriad of responses is insanely confusing and, for me, definitely contributed to my confusion/isolation after the diagnosis. It took a long time for me to counter other people's completely-uninformed opinions, but what I've found to really help is to remind myself of the facts:
1 - I received this diagnosis from a trained professional. The process was long and thorough, and I believe I did an equally sufficient job of representing how I may fit on the spectrum as well as how I may not.
2 - The ADHD assessment I took (two years later and, again, with a trained professional) also identifies ASD and the results of the assessment skew in exactly the way it most commonly skews for those on the spectrum.
3 - The people who knew me before I really leared to mask are the ones who see my diagnosis as obvious. The ones who knew me after I started drinking (I quit drinking 8 years ago) and while/after I learned to mask are the ones who doubt it most.
4 - The ones who doubt it have absolutely zero training and have done zero research into what it actually means to be on the spectrum.
5 - Exes (and my girlfriend at the time of the diagnosis) who I have actually lived with, the ones I still talk to, are the least surprised by the diagnosis. One, who is a therapist, even suspected it.
6 - The "most autistic" things I do, I keep out of the view of others. So, of course their perception will be skewed.
7 - Alcohol can really dampen the social aspects of ASD. I used to be a frequent and heavy-ish drinker in social situations. Which led me to quit, years before my diagnosis. As soon as I quit drinking, my social life and friend circle tanked. Anecdotally, this seems very common with folks on the spectrum who also drink socially.
I don't know if that helps, but it helped me tremendously to lay all of that out in a way that reduces the impact on my psyche as a result of others' doubt. And it also took me _years_ to really see that objectively in a way that's only beginning to put up an emotional/psychological boundary between what my uninformed friends believe and what I know to be true.
On top of that, if anyone wants to doubt me again, I have a solid list of things I can present. And they can choose to believe them or not. But I am now far more clear on where I stand and can be far less swayed/affected by another person's doubts.
I hope you're able to find a similar steadiness in it. It can be really hard, but if you can work through the process, it might be pretty rewarding and validating.
* Edited for clarity.