on best behavior

on one's best behavior

being as polite as possible. When we went out, the children were on their best behavior. I try to be on my best behavior all the time.
See also: behavior, on

on your best behavior

not causing any difficulties The two candidates were on their best behavior, giving serious answers to questions from a group of citizens.
Usage notes: usually used to refer to children, but also often used to describe the actions of adults in uncomfortable situations
See also: behavior, on