knuckle sandwich

Plural

knuckle sandwiches

used to refer to a punch that is hit in a person's mouth

The idiom "knuckle sandwich" originated in the early 20th century as slang for a punch to the face or a physical blow, often in the form of a fist to the mouth or nose. The phrase is a playful way of describing a violent action and is meant to sound more lighthearted than a real threat, despite its aggressive undertones.

When the schoolyard bully wouldn't leave him alone, he finally stood up and threatened to give him a knuckle sandwich.
The heated argument at the bar almost turned into a brawl, with one patron warning the other to watch out for a knuckle sandwich.
During the boxing match, the champion delivered a powerful punch to his opponent, essentially serving him a metaphorical knuckle sandwich.
In the comedy movie, the witty protagonist threatened to serve his obnoxious neighbor a knuckle sandwich as a humorous way to defuse the situation.
When the heckler continued to disrupt the comedian's act, the performer quipped that he might receive a knuckle sandwich if he didn't quiet down.