How is “dog eat dog” used?

In American Psycho II: All American Girl (2002), one line is: “It's a dog-eat-dog-world out there,”

Which movie is “dog eat dog” from?

The clip at the top of this page is from American Psycho II: All American Girl (2002).

It's a dog-eat-dog-world out there,

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a situation in business, politics, etc. where there is a lot of competition and people are willing to harm each other in order to succeed

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オックスフォード映画の 100%
a situation in business, politics, etc. where there is a lot of competition and people are willing to harm each other in order to succeed
...because of this new Anti Dog-Eat-Dog bullshit...
It's a dog-eat-dog-world out there,

定義：Oxford Advanced Learner's Dictionary 第 9 版