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2.
To criticize or disparage, often spitefully or unfairly.
Speaking unfavorable about.

Badmouth
by web dictionary April 18, 2013
 
1.
v., to curse or say negative things about something, usually another person.
Why did he want to bad mouth me?
by The Doctor September 17, 2004
 
3.
bad-mouth: say unkind, unflattering, embarrassing (and probably untrue) things about someone.
Iyad: "I don't believe what Ihab said. Why is he bad-mouthing

me?"
Reham: "He's probably jealous of your success."
by Iyad Private January 26, 2013