He has a big mouth. 他是个大嘴巴。
例句：
You'd better not tell him,he has a big mouth.
你最好不要告诉他，他大嘴巴。
Why did you tell it to everybody?I told you to keep a really have a big mouth.
为什么你把这个告诉所有人，我让你保守秘密的。你真是大嘴巴。
A:Congratulations.
恭喜你。
B:What?Why?
什么？为什么？
A:Mary told me that you and your boyfriend are going to get married.
玛丽告诉我，你和你男朋友要结婚了。
B:She really has a big mouth,I just told her yesterday.
她真是大嘴巴，我昨天才告诉她的。