be on one's best behavior

verb

Roget 944: be virtuous etc. adj.; practice virtue etc. n.; do one's duty, fulfill one's duty, perform one's duty, discharge one's duty; redeem one's pledge, keep one's promise etc. 926; act well, act one's part; fight the good fight; acquit oneself well; command one's passions, master one's passions; keep in the right path.    set an example, set a good example; be on one's good behavior, be on one's best behavior.    ... show more

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