Be on (one's) good behavior American verb phrase
Behave in a way that show respect and politeness
This is the first time I have met her parents, so I should be on my good behavior.
The kids promised to be on their good behavior for the new housemaid.
people often do irrational or foolish things when they are in love.
Used to describe someone kind, calm and pleasant
To stay out of trouble or avoid doing something wrong
Used when you threaten to harm someone in the same way as they harmed you
The verb "be" should be conjugated according to its tense.
White lie
Ken: Yesterday I lost the watch that my girlfriend presented to me. Should I tell her this thing?
Lily: Certainly Not! Your girlfriend will be angry with you. Children and fools tell the truth.