Young people seem really bad at "public greeting etiquette."
I.e, when walking in an uncrowded park or sidewalk, as you pass a stranger you make polite eye contact, which he returns. Whomever registers the eye contact 'second' says "hello" in passing.
But if you walk by anyone under ~45, they just completely botch this. They drop the ball. It's like they're dead to the world; total disinterest in their fellow citizen. I would wager that almost anywhere in the USA, if you walked around all day in non-crowded places counting the greetings you exchanged, ~80% of them would be with people over the age of 45. In the event you DO greet a person ages 18-45, you'll find they do not make eye contact, and appear extraordinarily uneasy about "stranger danger" or something like it.
And it makes you wonder -- what will the country be like if and when the last shreds of genteel warmth and decency among strangers have vanished?