In Full Metal Jacket (1987) the protagonist wears a pin with a peace sign but has "Born to kill" written on his helmet. I think he was trying to suggest something about the duality of man, sir.

The quote from the movie uses a racist slur to talk about the Vietnamese. It's supposed to highlight the contradiction between the mission of "helping the people" while the people that are supposed to be helping despise them, think of them as lesser, and kill their civilians

::: spoiler Edit: full scene transcript, including the slurs Colonel: Marine, what is that button on your body armor?

Joker: A peace symbol, sir.

Colonel: Where'd you get it?

Joker: I don't remember, sir.

Colonel: What is that you've got written on your helmet?

Joker: "Born to kill", sir.

Colonel: You write "born to kill" on your helmet, and you wear a peace button. What's that supposed to be, some kind of sick joke?

Joker: No, sir.

Colonel: What is it supposed to mean?

Joker: I don't know, sir.

Colonel: You don't know very much, do you?

Joker: No, sir.

Colonel: You better get your head and your ass wired together, or I will take a giant shit on you.

Joker: Yes, sir.

Colonel: Now answer my question, or you'll be standing tall before the man.

Joker: I think I was trying to suggest something about the duality of man, sir.

Colonel: The what?

Joker: The duality of man; the Jungian thing, sir.

Colonel: Whose side are you on, son?

Joker: Our side, sir.

Colonel: Don't you love your country?

Joker: Yes, sir.

Colonel: Then how 'bout getting with the program? Why don't you jump on the team and come on in for the big win?

Joker: Yes, sir.

Colonel: Son, all I've ever asked of my Marines is for them to obey my orders as they would the word of God. We are here to help the Vietnamese, because inside every gook, there is an American trying to get out. It's a hard-ball world, son. We've gotta try to keep our heads until this peace craze blows over.

Joker: [salutes] Aye-aye, sir. :::

Inside every American, there is a slur trying to get out.