watch意思是"觀察、注視"，back意思是"後背"，watch your back字面意思是"看你的後背」，其實意思是注意某人或者某事會對某人產生不利或傷害，要小心那些在你背後看不見的地方會出現的問題。
看看老外聊天時怎麼用watch your back：
A I heard you grew up in the inner city.Things were rough，weren't they？
B Yeah，it's a place where you have to always watch your back.
A 聽說你小時候住在舊城區。那邊環境很複雜對吧？
B 是啊。在那裡隨時都要小心周遭的危險。
watch your back例句精選：
With Messier you have to watch your back.
和米歇爾一起共事，你得多長一個心眼。
Watch your back in this place, it can be dangerous.
在這兒小心點兒，這地方可能很危險。
Make sure you watch your back with that guy.
要小心別被那個傢伙騙了。
提醒某人要注意某事，除了watch your back，還有如下表達：
Watch your step. 小心舉止。
Gina just lost her job，so watch your step.
吉娜剛丟掉工作，所以你別亂說話。
Play it safe. 保險一點。
In the end he decided to play it safe and not propose to her so quickly.
最後他決定保險一點，不要這麼快向她求婚。