be good
1. A set phrase urging one to behave. Kids, please be good for your grandparents this weekend.
2. A valediction. All right, see you next week. Be good!
Be good.
a departure response meaning "good-bye and behave yourself." Jane: Well, we're off. Be back in a week. Mary: Okay, have fun. Be good. Jane: Do I have to? Tom: Bye. Be good. Bill: See you next month.