I think it is more than just “kids being kids,” or “teenagers being subhuman assholes.”
I think they’ve been trained. Trained for decades to not respect parents, or anyone outside their peer group.
How? Have you looked at television programming targeted at children, ranging from very young to obnoxious?
With very few exceptions, programming portrays parents as incompetents, with fathers generally being incapable of the most simple tasks. There have been a few shows that went in a different direction, but the vast majority hate on the ‘rents, and mostly on Dad.
Why is this? The target audience for “youth entertainment” does like that, but… the conspiracy theorist who lurks in my hindbrain says that destroying the familial mentoring relationship between child and parent, and especially child and father, is a strategy to develop a youth which will be less likely to be guided by those older.
Couple that with the “everyone is going to pass this class, and get a special winner trophy,” and the kids have never learned to plan for failure. And they assume that anyone who does is courting failure. And since older people are, by definition, failures, they pat themselves on their backs at their limitless knowledge.