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on one's best behavior

idiom

: behaving very politely and well
The children promised to be on their best behavior.

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on one's ass
on one's best behavior
on one's breath
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“On one's best behavior.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/on%20one%27s%20best%20behavior. Accessed 7 Dec. 2025.

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