re: Millennials - of course the stereotypes don't apply to every individual, but they're largely true.
First off, as a definition - millennials are the generation after generation X, those born between 1980 (some say 1981) and 2000 - so a pretty wide spread, and someone born in the early 80s is going to be very different from someone born in 1999. It's the usual problem with generalization and defining things by "generation".
People born 2001-present aren't millennials - their generation hasn't been given a nickname which has stuck yet, mainly because the oldest ones are only 17, they're not adults, most aren't in the workforce or college yet, etc. "Generation Z" is the best they've got, but that will change to something else soon, no doubt.
Stereotypes that I've seen confirmed repeatedly;
Constantly on their phones. A favorite "trick" (which they don't seem to understand everyone is aware of) is to go into the bathroom with their phone for 15-20 minutes, taking extra breaks that they're not entitled to and making everyone else have to cover for them.
I've also had some younger people tell me they'd rather browse the web on their phone than a computer (even when a computer is right there) which just baffles me - since you've got the larger screen, much more powerful and customizable browsers, etc. on a PC. Same with watching movies - I mean, sure if you're on a plane or waiting somewhere, but watching a movie on a phone when there's a much larger screen available? Weird.
I've had to explain to some younger co-workers too that, no, taking 1 sick day a month (every month) isn't really acceptable and the company will never see it that way. 12 per year? Fuck... I mean 4 per year maybe... Only talking about unscheduled absences here, not scheduled vacation time etc. - but they don't seem to see the difference, don't get how we can plan for coverage of your duties if we know you're going to be out a week on vacation, but not if it's a random sick day, etc.