put the bad mouth on

all mouth and no trousers

Alternative form of all mouth and trousers.

all mouth and trousers

Superficial, engaging in empty, boastful talk, but not of real substance.

all one's taste is in one's mouth

One lacks good taste in aesthetic or cultural matters.

bad actor

An individual or entity with a prior criminal conviction, or who has been sanctioned by the court or regulator.

bad apple

A person who is not wholesome, honest, or trustworthy, especially one who has an adverse influence on others.

bad books

Disfavor.

bad business

Synonym of bad news (“irritating, troublesome or harmful thing, situation or person”).

bad company

The wrong crowd.