Superlative form of 'chuff' when used as an adjective meaning most pleased or delighted (British slang); most puffed out or cheek-distended.
Superlative of 'chuffed' (British slang for 'pleased'), formed with '-est' suffix. 'Chuffed' may derive from 'chuff' meaning to swell or puff out.
British slang 'chuffed' (pleased) might come from the image of puffing out your cheeks when happy—language preserves these physical gestures that speakers use to express emotion.
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