1. Expression： sly dog

Explanation：Someone who, through cunning, devious, or dishonest means, achieves a fortuitous outcome. （偷鸡摸狗者，阴险狡猾的人）

Example：——We should keep Frank at arm's length. ——Yeah. He's known as a sly dog. He's done many people in.

——我们应离Frank远一点。——是的，他阴险狡猾出了名，经常陷害别人。

Susan is a sly dog and we can' t depend on her.

苏姗是个狡猾的人,我们不能依赖她。

He was beginning to believe that he had a sly dog to deal with indeed.

他开始感到他的这个对手实在很狡猾。

What a sly dog! He managed to get a copy of the test so he could memorize the answers ahead of time!

他真狡猾，搞到了一份考卷，这样他就能提前把答案背下来了!

2. Expression：yellow dog

Explanation：A despicable person or thing. （卑鄙的人或事）

Example：I can't believe you get so invested in these debates—all politicians are yellow dogs that can't be trusted.

我真不相信你在这些辩论中如此投入——所有的政客都是不能信任的狗杂种。

3. Expression：a big dog

Explanation：An important person. （重要的人）

Example：On arriving at the party, he saw a big dog. Then he went up and offered his hand, but he was proud and did not take it.

他一到交际会便看到一位要人，后来他走上前去主动伸出了手，但那位要人傲慢，未曾接受。

Come off your perch and stop considering yourself as the most biggest dog here.

别狂妄了，不要自以为这儿你是老大。

He really seemed to look upon himself as biggest dog in the parish.

他那个派头，俨然整个教区首屈一指的人物了。