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rat (one) out
To inform an authority figure of one's bad or illegal behavior. I can't believe you ratted me out like that to Mom and Dad—I'm never telling you anything ever again! The criminal ratted out his accomplices to avoid jail time.
Sl. to quit; to fink out (on someone or something). It's too late to rat out. He tried to rat out at the last minute.
To expose or reveal incriminating or embarrassing information about someone: The newspapers ratted out the people who were involved with the scam.
in. to quit; to fink out (on someone/something). He tried to rat out at the last minute.