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.