be sharp-tongued but not malicious 有口无心

“有口无心”，汉语成语，意思是嘴上说了，心里可没那样想。指不是有心说的（say what one does not really mean），可以翻译为“be sharp-tongued but not malicious”。

例句：

他是个直来直去的人，说话有口无心。

He's a blunt man, often speaking sharply but meaning no harm.

他这个人有口无心你是了解的。

You know what he is like. He says whatever enters his mind.