rap one's knuckles
rap one's knuckles {v. phr.}
To scold or punish.
The principal rapped our knuckles for cheating on the test.
If you talk back to Dad, you'll get your knuckles rapped.
The club got its knuckles rapped by the principal for hazing new members.
Why rap my knuckles? It wasn't my fault.
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Source: A Dictionary of American Idioms