say a mouthful
1. {v. phr.}, {slang}
To say something of great importance or meaning; say more by a sentence than the words usually mean. — Usually in past tense.
Tom said a mouthful when he guessed that company was coming to visit. A dozen people came.
2. {v. phr.}, {informal}
To vent one's honest opinion, even in anger.
He sure said a mouthful when he told his boss what was wrong with our business.
Contrast: GET AN EARFUL.
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Source: A Dictionary of American Idioms