A few years ago these kids would have been goths or punks, new romantics, mods, teddy boys...
My dad loved philosophy and usually had a relevant quote (he often quoted the 'Socrates' comment).
These seem suitable:
"They [Young People] have exalted notions, because they have not been humbled by life or learned its necessary limitations; moreover, their hopeful disposition makes them think themselves equal to great things - and that means having exalted notions. They would always rather do noble deeds than useful ones: Their lives are regulated more by moral feeling than by reasoning - all their mistakes are in the direction of doing things excessively and vehemently. They overdo everything - they love too much, hate too much, and the same with everything else. (Aristotle)
"The world is passing through troublous times. The young people of today think of nothing but themselves. They have no reverence for parents or old age. They are impatient of all restraint. They talk as if they knew everything, and what passes for wisdom with us is foolishness with them. As for the girls, they are forward, immodest and unladylike in speech, behavior and dress."
(From a sermon preached by Peter the Hermit in A.D. 1274)
"I see no hope for the future of our people if they are dependent on frivolous youth of today, for certainly all youth are reckless beyond words... When I was young, we were taught to be discreet and respectful of elders, but the present youth are exceedingly wise [disrespectful] and impatient of restraint". (Hesiod, 8th century BC)
"I believe what really happens in history is this: the old man is always wrong; and the young people are always wrong about what is wrong with him. The practical form it takes is this: that, while the old man may stand by some stupid custom, the young man always attacks it with some theory that turns out to be equally stupid." (G.K. Chesterton)
'The children now love luxury; they show disrespect for elders and love chatter in place of exercise. Children are tyrants, not servants of the households. They no longer rise when their elders enter the room. They contradict their parents, chatter before company, gobble up dainties at the table, cross their legs, and tyrannize over their teachers.' possibly Socrates