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).

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

Heard in 4 movies

Oxford100% of films
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,

Definitions from the Oxford Advanced Learner's Dictionary, 9th edition

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

Said in 6 films · #1