I spent a lot of time in therapy. I've learned to keep more quiet about things that seem obvious to me because I do at times miss the fact that what is obvious to me is something someone else thinks they are very cleverly hiding or some crap. Like anyone, I have something of a tendency to assume that what is obvious to me is obvious to others.
An awful lot of so-called social skill appears to be knowing what polite lies you are supposed to collude with to make the people around you comfortable. This is actually the root cause of the persistence of a lot of social ills.
If you can't tell someone "Yeah, that's racist/classist/sexist baloney, give me a break" because that's too rude to tolerate, don't be all shocked when the world is overrun with racism, classism, sexism, etc.
Abusive people also count on normalizing their ugly behaviors and on people around them not saying "No, dude, that's not funny at all. Stop that." We have movie scenes where some child is hiding from a visiting aunt and her icky slobbery kisses and tendency to pinch his cheeks hard and the parents giggle about the behavior of the child rather than tell the aunt "Bitch, keep your hands to yourself. No, you don't have a right to do this to my child. They don't like it, so don't do it."
And then we are all mystified at how to stop child molesters. But you can't tell people "Um, yeah. You are actively colluding with child molesters when you do stuff like that."
Because that would be rude. Or something.
In the given example, it may be apparent to the child that mum is angry/annoyed. But they are likely to be confused as to why.
(which is where DoreenMichele's point about educating the parents comes in - if they can clearly articulate how they feel and why in a given situation, then the autistic child is likely to be able to learn and remember this, even if it might take them a few repetitions of the situation for it sink it (like anyone learning anything that isn't intuitive to them))
It almost seems as the opposite was true where telling of intention and desire is _extremely accurate_, to a scary degree, if it's interpreted through text or speech. But where body language and weird social norms/white lies that are important social queues for me go completely unnoticed.
If people not on the spectrum actually understand others intentions and desires more, and not just have the ability to read it from social queues people on the spectrum don't pick up, what does that say about so many people acting in selfish and mean ways if it benefits them?