bad mouth

基本解釋

The mouth of unforgiving, generally very soft hearted. My heart is getting, the mouth will speak. So good heart good, bad mouth good.
嘴上不饒人的，心腸一般都很軟。心里不饒人的，嘴上才會說好聽話。所以好人心善，壞人嘴善。
Don't bad mouth me.
別說我壞話。

For example, if you say bad things about a person, the person might protest and say "Do not bad mouth me."
He might say that experience "left a bad taste in my mouth."

Aside from refusing to ever hire you again, executives have long memories and will bad mouth you any chance they get.
FORBES: Magazine Article
You pause, remind yourself that an employer (via its employees) cannot bad mouth you, breathe a sigh of relief and complete the application.
FORBES: Tips for Tackling a Tarnished Reputation
Since Apple has fallen behind in OLED technology, it makes sense for Apple to bad mouth OLEDs while behind the scenes scrambling to catch up.
FORBES: Tim Cook Does Not Like OLED But Spends Money On It