It's never a good idea to bad-mouthsomeone, because that other person may hear you, or people that you are talking to might tell that person - especially if that person is your boss!
Full of energy, upturned mouth. The pain of sorrow and disappointment hidden behind the smile. Some people say bad things about someone in front of you, you just smile.
精神饱满，嘴角上翘。将痛苦忧愁与失望藏于微笑后面。有人在你面前说某人坏话时，你只微笑。
3
"To bad-mouth (someone)" means to say bad things about another person.