1.
show-off, clown, person who gets carried away
A person who easily gets caught up in the mood and acts silly or boastful to entertain or impress others. Often used with a mix of affection and mild criticism.
お調子者 describes someone who easily gets carried away by the mood and acts silly, boastful, or exaggerated to entertain others. From 調子 (rhythm, condition) + 者 (person), with a prefix お that is part of the word rather than a mark of politeness.
Common patterns
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Can be affectionate or critical depending on context. When said with a smile, it means "class clown" or "life of the party." When said with annoyance, it means someone who goes too far or cannot be taken seriously.