potty mouth

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 taste in one's mouth

A feeling that something is morally despicable as to cause nausea.

big mouth

The mouth of someone who talks too much, especially by making exaggerated claims or by inappropriately revealing information.

born with a silver spoon in one's mouth

Born rich, or into a wealthy family.

butter wouldn't melt in someone's mouth

The identified person appears to be benign, mild-mannered, or calm (but with an integral suggestion that, to the contrary, they really are untrustworthy, disagreeable, or mean-spirited).

down in the mouth

Sad or discouraged, especially as indicated by one's facial appearance.