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

例句

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.

请注意

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。

例句

My boss won't give me a pay rise - he's got a real mean streak.