to lead a dog's life 形容人过着贫困潦倒、惨不忍睹的生活
Tom's been leading a dog's life since he got divorced.
汤姆自离婚后一直过着混沌潦倒的日子。

dog eat dog 残酷、竞争激烈
Some people say we live in a dog-eat-dog world.
有人说，我们生活在一个竞争激烈的世界。

work like a dog 指一个人努力、卖命地工作
They say that to be successful, a person has to work like a dog.
他们说，一个人想要成功就得拼命工作。

dog-tired 筋疲力尽
Such hard work can make him dog-tired.
如此坚辛的工作使他疲惫不堪。

sick as a dog 病得严重
The situation would be even worse if she became sick as a dog.
如果她病得厉害，情况会更糟。

Every dog has its days.每个人都有属于自己的运气/每个人都有时来运转的一天
Don't give up and try your best I believe every dog has its day.
不要放弃，继续努力，我相信每个人都会有成功的时候。