dog eat dog字面意思狗咬狗，引申为残酷无情的竞争；自相残杀。

【例句】
I'm afraid in this line of work it's a case of dog eat dog.
恐怕在这种行业中竞争是残酷无情的。

With shrinking markets, it's dog eat dog for every company in this field.
由于市场的萎缩，这些公司展开了你死我活的竞争。