YABU - The first example is silly. The parent should be grateful and showing appreciation. I personally wouldn't come write an MN thread over this. If id known you were the type to write a thread like this, over that example, I wouldn't feel confident having my child come round. I imagine the mum is none the wiser as to your thoughts. If the kid is consistently rude and difficult, then fair enough, but this?
The second example, if it were me, I'd challenge the child on no response. Are you ok? I was just asking x,y,z. They aren't mutants and I imagine this is not beyond them. I do this and it's fine.
I find we have the opposite problem to what you're highlighting. That is parents who are so devastated about how they appear as mums, how they are judged and what others think of them. This post exemplifies it, wherein people are desperate to show they are good mummies and seek validation. It kind of gets in the way of the important stuff.
The place where I see room for some to really stress about this is in teaching. I see some posts regards very difficult pupils and if the parents aren't helpful, I see that as a potential growing problem.
Whoever said all kids are just ND these days, also pretty silly really. Do we have an influx of data on incorrectly diagnosed children or adults? I'll hazard a guess that we don't. I don't understand why this reality is so scary.
ND kids are not incapable of manners either.
Appreciate that if mums removing a flailing child under her arm like a handbag ( been there), then you're understandably not going to get a thankyou Mrs Doodah for the scrumptious cookies.