The dismissiveness hurts.
I haven't told very many people, but reactions from most that I have told came in one of two varities: a. not possible; b. I would never have thought that [subtext: I may be tentatively willing to believe you, but I'll expect you to keep acting fully NT at all times, and I won't see this as an explanation for why you sometimes fail to act entirely NT and will, at times, continue to fail at it].
Category a. has barely the faintest idea of what AS and the autism spectrum are, but for all its ignorance adheres to misguided popculture myths about them. Those restrictive stereotypes rarely fit, hence people's incredulity. In fact, popculture seems to confuse the autism spectrum with sociopathy quite a bit, from what I'm seeing, in claiming that we see people as objects and have no empathy (i.e., traits around which sociopathy centres), even though autism spectrum conditions and sociopathy appear to me to be rather more polar opposites than confusingly close.
Category b. acknowledges to a varying degree that they don't know everything about the autism spectrum, but really, since you're acting NT - however high the price tag for doing so may be - you may as well be expected to keep up and refine the act rather than expect them to understand that it has its limits. They don't see the effort that goes into it (other than perhaps noting, annoyingly puzzled, from time to time that you often seem exhausted), so it can't really exist. A simple mental act of transference might give them some insight: if you look, many people should be able to unearth a rough analogy from their own lives and experiences sooner or later. But autism, specifically, is not their problem, and it's rare as far as they know, so they can't be bothered.
Personally, I couldn't keep up the act if I didn't impose limits: no, I won't go out for drinks with you after work; no, I don't care that you think it's important to socialise with colleagues (and I don't agree that it is, incidentally); I work to survive, not to get out of the house and for a ready-made social circuit; no, won't discuss my private life and my interests with you extensively, and I'll make hearing about yours as short as socially acceptable (by your standards).
I don't actually say those things to colleagues, but I act on them - quite nicely, actually, I think. I'm not trying to hurt anyone, but I'm also trying not to get hurt entirely too much, considering that putting on as much of an act as I do is itself damaging already.
(As an aside, when I mention my interests, they're mostly 'wrong' anyway because they're things people have been trained to think of as 'work', not 'downtime'. I've learned that people are then prone to consider me ambitious. I'm not, at least not in the status-pursuing sense that NTs think of it. I like to learn for the sake of understanding things (and also eternally in hopes of one day earning a living in a way that isn't the worst possible for me), and even though it can make me tired, it makes me tired in a good way. It feels markedly different from the plain exhaustion of keeping up an act. As someone said upthread, NTs often appear to see everything in terms of power-dynamics.)
People have mentioned to me too that 'everyone puts on an act', 'everyone gets exhausted', 'everyone doesn't always feel like going out', etc. While that's correct, it also epitomises just how intensely people want to deny that autism is a 'thing'. The act that 'everyone puts on' isn't usually, as far as I can tell, for mere survival (e.g. so you can get and keep a job, any job, just to live). It's for social or career advancement - not just to be identified as fully human and somewhat capable. 'Everyone gets exhausted' not just by existing in this world. NTs get exhausted because they're doing as much as possible striving for status in a world that is built to their needs. Not because their senses are constantly under assault while they're consciously trying to act like... velociraptors to other NTs, because acting like a velociraptor is normal and necessary. 'Everyone doesn't always feel like going out' because they've been burning the candle at both ends for a while, not because there's nothing in it for them by going out besides more sensory assault, added expense and the eternal threat of making your social situation more dire than before because you're acting wrong and refusing to talk about celebrity pregnancies, someone's beach holiday in a fascinating country of which they learned nothing while there or whatever else the braindead nonsense du jour is.
The problem with these descriptors of [fill in the blank] that 'everyone is/does' is they're vague. They're unspecific catch-alls. Yes, everyone gets exhausted, just like everyone will experience pain. But all pain is not equal - a point that, I think, no NT that I know would argue against - while arguing quite persistently that all exhaustion generally is. (Well, society at large makes an exception for parents, who are allowed more exhaustion than others, independently of any one individual's circumstances.)
They don't see the work we do, therefore it doesn't exist. If nothing were known about the autism spectrum, they might be forgiven. But that's not the case. If I give them a frame of reference that is (rather easily, I might add) verifiable as a 'thing' for why I don't function like them, people who claim a vaguely amicable association with me should be in a position to give it five to fifteen minutes of their time, once in their lives, to try to understand. They do fiddle with their phones an awful lot. Phones that can access any of the same sites available to me, and an awful lot of academic articles on the autism spectrum (though I wouldn't endorse all academic articles on autism wholesale by virtue of them being academic - there's a lot of confusion, muddled thinking, bias and agenda-setting in academia, too. But it would still be considered the best source of objective information by most).
In light of all this, I don't say too much about it anymore. I've told a couple of colleagues in the past, and despite initally positive reactions they've squarely landed in category b. (above) over time. People really just want you to function the way they think people function. Even highly educated people aren't often critical thinkers, I've found. And, in true NT fashion, people tend to treat education as a game to get ahead, not to actually learn stuff that might apply to, you know, life. So, much of the knowledge gained professionally or for professional purposes is somehow shut off from access for private or social use. I find that very ironic, especially the social bit for NTs. (Random example: I've had a well-paid, particularly intersectionally privileged researcher on social inequality (!) complain to me that their taxes were too high. Incidentally, by virtue of earning so much, their taxes were lower than mine, in terms of a percentage of income (with me also being less intersectionally privileged, therefore less likely to become a high earner). This is not an isolated example.)
It's frustrating. You shouldn't have to keep being on the autism spectrum a secret or deliberate about whom you tell, but at the same time, you're unlikely to always have the spoons to deal with people's abrasive, uninformed, ignorant reactions.