tell tales
idiomPart oftale
tell tales — idiom
1. To reveal someone's secrets or bad behaviour to a person in authority, often wit
1.idiom
Definition
To reveal someone's secrets or bad behaviour to a person in authority, often with the result of getting that person into trouble.
Example
If you tell tales on your classmates, they will not want to work with you on group projects.
Vikram got into trouble for telling tales about his younger brother stealing cookies from the kitchen.