Maybe in some places. But when I go out to a restaurant, I'm often surrounded by a few dozen other diners, and no one is acting up or shouting at waiting staff. I have seen customers be obviously rude to staff but it's very rare compared to the number of "normal" interactions. Sure not everyone is friendly and totally polite, but entitled, shouting or just being an ass is an absolute exception, like less than 0.1%. I also worked as a waiter in a couple of different restaurants over a two year period, and don't remember any incidents either to me or my colleagues.

When I read comments like this it makes me wonder if I've been lucky enough to live and work in decent places, and the USA is just an nightmare hellscape, or if the reality there is much more normal and we just hear an unrepresentative sample of it.