Ruthlessly competitive: “You have to look out for your own interests; it's a dog-eat-dog world.”
dog eat dog
Ruthless acquisition or competition, as in With shrinking markets, it's dog eat dog for every company in this field. This contradicts a Latin proverb which maintains that dog does not eat dog, first recorded in English in 1543. Nevertheless, by 1732 it was put as "Dogs are hard drove when they eat dogs" (Thomas Fuller, Gnomologia).