rap somebody over the knuckles
rap (one) over the knuckles
1. Literally, to smack someone, especially a child, on the knuckles as a punishment for misbehavior. The teacher was fired for rapping students over the knuckles when they spoke out of turn.
2. By extension, to give someone a warning, verbal scolding, or a minor punishment. The public was outraged that the government merely rapped the company over the knuckles for illegally dumping chemicals in the river. The boss rapped my knuckles for coming in late on Friday.