While I am on a tear about boomers, and what I see as a generational epidemic of self-centeredness, I think it’s really interesting to understand how/why some of them currently see gen Z as the selfish ones.
Getting old enough to exit what older folks mean by "kids these days" has exposed me to more of their unfiltered thinking in this realm.
Like when boomers get called selfish, we can point to all of this data about how they have clung to power instead of stepping aside, how they pilfered an unsustainable economic system and closed the door behind them as they went.
Whereas when they say that "young people now" are selfish, what I've heard cited amounts to...
Wanting to be free from constant surveillance and control. (I'm talking about ADULTS saying this too.)
Demanding that personal boundaries be respected.
Asking that they get to be called by the name and pronouns that they would like to be called by.
Consequences for saying bigoted things.
Wanting an economic system (AND EVERYTHING ELSE) to be sustainable for the future.
Not wanting to work their lives away.
Not wanting to be saddled with student loan debt that goes towards degrees that have little real value in the current hiring job market. 
OH DAMN I forgot the big “Not wanting to have kids they can’t afford.” The amount of boomer “you owe me grandkids” open chatter is grosssss.
What they're actually mad about is that we're not collectively suffering in silence about everything they've fucked up until after they're dead and gone, which is what they told themselves would happen.
They justified the damage they've done by telling themselves that they can reap the short term rewards for their corrupt and damaging economic and political policies and their children and grandchildren would simply fix the damage done once they were gone.
[As they've convinced themselves as a generation that They "fixed" all of society's ills and previous generations problems in the 60s and 70s and have been patting themselves on the back for the marginal progress achieved ever since even while actively dismantling that very same progress because it no longer suits them]
We're "selfish" for holding Them accountable for the damage They have done and expecting them to Do Something to correct things instead of nobly shouldering the burden of their mistakes until they're all dead so they can enjoy their "Golden Years" living like Kings.
