After two friends return home from the Vietnam War one becomes mentally unstable and obsesses with becoming a bird.

Birdy: Flying is much more than flapping wings. A bird can flap its wings and not move an inch then when it wants to fly the slightest flick of its wings sends it up against the sky. You have to feel that air has substance and can hold you up. It's mostly a matter of confidence.
Birdy: Do you like pigeons?
Sergeant Al Columbato: What's to like?
Birdy: They fly.
Sergeant Al Columbato: They fly. So what?
Birdy: That's enough.
Doctor Weiss: You mean the spitting?
Sergeant Al Columbato: Yes.
Doctor Weiss: The army left a bad taste in his mouth.
Birdy: There's nothing in my life to keep me here anymore. I wish I could die and be born again as a bird.
Birdy: I'm starting to worry that I'll never really fly the way I've been going. As scary as a bird's life must be... at least they have that. They can always fly away.
Birdy: You ever wondered what our lives down here must look like to a bird?
Birdy: I guess it's kinda hard to be good at something nobody wants, huh?
[about his psychiatrist]
Sergeant Al Columbato: I don't trust the guy. Everything's too interesting to him.
Birdy: In a dream, I'm trying to decide what I am. When I sleep I'm giving myself strength. I'm reaching for the force to fly. Perta waits, cups herself to receive me. I hover then lower myself into her. Perta and I become one. I see through her eyes, fly on her wings. I am no longer alone.
Sergeant Al Columbato: You ain't gonna fly any more than I could, Birdy.
Birdy: The reason you couldn't fly, Al, is you don't believe you could fly.
Sergeant Al Columbato: Maybe life is shitty. It is shitty. I'll tell you something. I'm not trying to pin life anymore. I don't even fucking understand it. I just want to make it through with some dignity, like everybody else. Of course, if there was any real dignity, there wouldn't be any sex.
[reaction to Al extolling the female breast]
Birdy: They're just like on a cow, but in a more stupid place.
Birdy: The dream is as real to me now as my waking life. I don't know where one begins and the other ends. I wish I could tell Al, but I'm afraid to. In my dreams, nothing holds me down. Everything's out and away. There's nothing in my life to keep me here anymore. I wish I could die and be born again as a bird.
Sergeant Al Columbato: You always were hard to hurt, Birdy. Real losers never hurt.
[last lines]
Birdy: [to a surprised Al, who was expecting to see Birdy dead] What?
Birdy: Al, sometimes you're so full of shit.
Birdy: Last night I flew. I really know what it feels like to fly.
Sergeant Al Columbato: Oh, you flew? How you flew?
Birdy: Well, I'm not sure. It's not something you can really take apart. When I fly, it's like in a dream. Only it's not a dream. The thing is, Al, you can't really put it into words. You just kind of have to feel it.
Sergeant Al Columbato: You're telling me you can fly like a bird?
Birdy: When I fly, Al... I am a bird.
Sergeant Al Columbato: This is getting too weird, Birdy. You gotta stop it with this.
Birdy: I thought if anybody would understand it would be you, Al.
Sergeant Al Columbato: Well, I don't. I don't even wanna hear about it.
Birdy: Why?
Sergeant Al Columbato: Because I'm tired of it! We used to have fun together. Now you are always off by yourself flying around inside your goddamn head! I hope this dream or whatever it is goes away. I think it's bullshit.