I wasn't trying to bad mouth your family. I was only telling my mom what had happened.

我不是想说你家人的坏话！我不过是跟我妈说所发生的事罢了。

youdao

The mouth of unforgiving, generally very soft hearted. My heart is getting, the mouth will speak. So good heart good, bad mouth good.

嘴上不饶人的，心肠一般都很软。心里不饶人的，嘴上才会说好听话。所以好人心善，坏人嘴善。

youdao

It is bad manners to talk with your mouth full.

嘴里塞满了东西跟人说话是不礼貌的。

《牛津词典》

For example, if you say bad things about a person, the person might protest and say "Do not bad mouth me."

VOA: special.2010.06.20

He might say that experience "left a bad taste in my mouth."

VOA: special.2010.06.20

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