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。

• I invited my friend rock climbing at the weekend, but he refused. I told him to get rid of that yellow streak and show some courage!
• 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.