Tell your brother to watch his back.

让你哥哥小心点。

One way and another, he had learned to watch his back when he crossed the road.

不管怎样，博格丹已经知道在穿过马路时要注意自己的身后。

There's one of you. There's 2 of us. I think you're the one who needs to watch his back.

你只有一个人。但我们有两个人。我觉得该小心的人是你。

Derrick Rose better watch his back.

德里克·罗斯可要防着你了。

Jared Kushner better watch his back.

贾德·库斯纳最好要提防一下了。