Definition
To behave with exceptional politeness and propriety, especially in a notable situation.
表現得體，力求完美
She knew she needed to make a good impression on her new boss, so she was on her best behaviour.
她知道需要給新老闆留下好印象，因此表現出最佳的行為舉止。
We always try to be on our best behaviour when we are at our grandparents' house.
我們在祖父母家時，總是盡量表現出最佳的行為舉止。
At the formal dinner, all the guests were on their best behaviour.
在正式晚宴上，所有賓客都表現出最佳的行為舉止。