on one's best behavior
Also, on one's good behavior. Very polite, as in Mother told the children to be on their best behavior during Grandma's visit, or The whole staff were on their good behavior while the client inspected the premises. [Late 1600s]
Words nearby on one's best behavior
on occasion,
on one hand,
on one's,
on one's account,
on one's behalf,
on one's best behavior,
on one's doorstep,
on one's feet,
on one's good behavior,
on one's guard,
on one's hands