Wearing cuffs or having been struck about the head and ears (slapped).
From 'be-' plus 'cuff' (from Old Norse 'kúfa', a glove or mitten, later meaning the edge of a sleeve, then a blow to the head). The word can mean either 'wearing cuffs' or 'struck repeatedly'.
A 'cuff' on the ear is a classic playground punishment, and 'becuffed' means you've been hit about the head—the same word works for both the decorative clothing cuff AND the violent blow, which shows how English reuses words to describe completely different things.
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