to stop doing something that annoys you.

The boys were making too much noise, so I told them to knock it off.

Usage notes: usually used as an order:

Knock it off! I'm tired of your teasing.

• the pearly gates
• the pedal to the metal
• the pen is mightier than the sword.
• the penny drops
• the person in the street
• the pick of
• the pick of something
• the picture of
• the picture of something
• the pink pound
• the plot thickens
• the plot thickens.
• the point of no return
• the pot calling the kettle black
• the power behind the throne
• the powers that be
• the primrose path
• the prodigal son
• the promised land
• the proof of the pudding .
• the proof of the pudding
• the proof of the pudding is in the eating
• the proof of the pudding is in the eating.
• the pros and cons
• the rank and file