Your translation, "Donde las dan. las toman", would actually be the phrase 't i t for tat' in English. This is used to describe when two sides keep performing similar acts of revenge on each other for no other reason than the revenge itself. I didn't send him a birthday card because he didn't send me one. Cut throat and dog eat dog describe a ruthless or merciless environment. Politics is a dog eat dog world. Financial trading is a cut throat business. So you need an idiom that means something like this, if there is one.

Beats me! 🤷‍♂️ Se trata de un perro-come-perro mundo ahí fuera.

Is there another idiom with the same meaning that could be translated or similar to another in Spanish? and If not, would it be right to say "Donde las dan. las toman." in my country or is there a better option?