I don't have much complaints about the younger workers when the wife and I get take out, go to restaurants, or shop.
Maybe it's my part of the country (upper Midwest), but most young people we meet in these places are usually very well-mannered, courteous, and friendly. I've yet to meet one who was obnoxious/rude. And they do a good job.
The worst situation with a young person behind the counter I can remember was in England some years ago. I went into a convenience store to get a drink or snack.
After finding my item, I went to the counter to pay. Behind the counter was a young person, male I would guess of Pakistani or Indian descent.
He was reclining on his chair (he had it tilted back as far as it could go without collapsing) behind the counter and talking on the phone to one of his friends as he rang up my purchase. He never said a word to me, not "thanks for shopping here" or whatever. I gave him an evil look after paying and left the store. I've never seen anything like that in any American place of business.
I very much would have liked to have kicked the chair out from underneath him, but I'd probably still be in some English jail or prison.