What is the origin of the idiom "knuckle sandwich" and when to use it?

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.