TONY: End yer sufferin', little man. Why don't you just pack up yer gear an' move out?
RIFF: 'Cause yer ma's hot fer me... It's 'cause I hate livin' with my buggin' uncle.
TONY: Come on! Uncle! Uncle!
MARIA: My brother is a silly watchdog.
BERNARDO: Ah, my sister is a precious jewel.
Brother and sister teasing each other, and thinking that nothing in their world is going to change. It breaks the heart knowing how wrong it's all going to go.
RIFF: Dear kindly Sgt. Krupke Ya gotta understand It's just our bringin' upke That gets out of hand!
Riff gives the age-old lament of the young: adults don't get them, and they usually end up doing more harm than good.
ACTION: Juvenile delinquency is purely a social disease.
RIFF: Hey! I got a social disease!
Of all the characters in the film, Riff is the one who really feels the most youthful: the guy for whom the world is his oyster, and there's no problem so big it can't be laughed away.
DOC: When do you kids stop? You make this world lousy!
ACTION: We didn't make it, Doc.
This is a surprisingly astute observation from a no-good street punk, and if you've ever been young, you know exactly how it feels. Grown-ups wrecked the world, and then pass it on to their kids with the assumption that those problems are all the kids' fault.
ACTION: When you was my age? When my old man was my age, when my brother was my age... You was never my age, none of ya! And the sooner you creeps get hip to that, the sooner you'll dig us!
DOC: I'll dig you an early grave, that's what I'll dig.
These kids only see Doc's age; they can't imagine that he might once have been feeling what they're feeling. Action doesn't believe in "older but wiser."
MARIA: Make it not true, please make it not true!
Remember when we asked when each character lost their youth? This is Maria's moment: a horrible, inescapable fact that she can't wish away and that she just has to deal with. Her beloved killed her brother.
TONY: Doc, I'm in love!
DOC: And you're not frightened?
TONY: Should I be?
DOC: No. I'm frightened enough for the both of us.
Being old means knowing just how many ways the world can destroy you. Tony hasn't figured it out yet. Sadly, the learning curve's a trifle steep.
DOC: Why do you kids live like there's a war on?
It's a good question and it doesn't have an answer. Just more dead kids and shattered innocence that Doc couldn't prevent.
TONY: Do you know what we're going to do in the country, Maria and me? We're gonna have lots of kids. And we're gonna name 'em all after ya.
DOC: Wake up! There is no Maria, Tony.
Tony is maybe the only character in the film who holds onto some remainder of his innocence until the end. He still hangs onto the hope that they can get away and live together, right up until the moment he dies.