rat on

rat on (one)

To inform an authority figure of one's bad or illegal behavior. I can't believe you ratted on me like that to mom and dad—I'm never telling you anything ever again! The criminal ratted on his accomplices to avoid jail time.
See also: on, rat
Farlex Dictionary of Idioms.

rat on someone

Inf. to report someone's bad behavior to someone in authority; to tattle on someone. John ratted on me, and I got in trouble. If he rats on me, I'll hit him!
See also: on, rat
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

rat on

Betray a comrade by giving information, as in He ratted on his best friend to the police. [Slang; early 1900s]
See also: on, rat
The American Heritage® Dictionary of Idioms by Christine Ammer.

rat on

v.
To disclose incriminating information about someone; betray someone by giving incriminating information: The hoodlum ratted on the rest of the gangsters. It was mean of you to rat on your friends.
See also: on, rat
The American Heritage® Dictionary of Phrasal Verbs.
See also:
  • rat (one) out
  • rat on (one)
  • rat on someone
  • rat out
  • ratted
  • going to tell
  • tattle
  • going to tattle
  • grass on (one)
  • grasse