用a yellow streak表达“胆小如鼠”

如果说某人has a yellow streak，那意思就是此人比较胆怯、不勇敢。

• We went rock climbing at the weekend. I loved it, but my friend refused to try it. He’s got a real yellow streak.
• The public accused the government minister of having a yellow streak after he refused to answer some difficult questions.

值得注意的是，如果一个人has a mean streak，那此人会经常做出卑劣、尖酸刻薄的事情。

• My boss won‘t give me a pay rise – he‘s got a real mean streak.