The everyday English phrase 'Dog eat dog' is most often used in a business environment or in any field involving competitiveness, such as in sports.
The everyday English expression 'Dog eat dog' implies that the persons involved are so fiercely concerned about their own interests, that they will aim at and achieve success out of the sheer determination to attain those interests; they are thereby 'eating' (defeating) their equally fancied opponent/rival.
1. Malini told her friend Manisha that unless she spoke up for herself, she would not get the promotion as it was a dog eat dog world.
2. The potential bidders for the soccer teams showed their true colours at the auction, practically shouting at each other and generally proving that dog eat dog.
3. The coaches and managers of the rugby teams got into a scrap over the goal and it turned into a full-fledged brawl. The two referees watching agreed that it was a dog eat dog situation.