He's always shooting his mouth off.

他老是信口开河。

If he hadn't shot his mouth off, things couldn't have been so awkward.

要不是他多嘴，事情也不至于搞僵。

If you mouth off, I will ground you for three weeks.

你敢顶嘴，我就三个星期不让你出门。

But we can't have Ethan running his mouth off about Amelia.

但我们不能让伊桑对阿米莉亚的事说三道四。

If you mouth off during class you will be in a lot of trouble.

如果你在上课的时候大发议论，你会有很多麻烦。