be on (your) best behaviour

British & Australian, American & Australian

to behave very well, usually because you are in an important or formal situation.

Now children, I want you all to be on your best behaviour when grandma arrives.

• give someone the bird
• give someone the boot
• give someone the cold shoulder
• give someone the creeps
• give someone the elbow
• give someone the evil eye
• give someone the finger
• give someone the glad eye
• give someone the green light
• give someone the heave ho
• give someone the heebie-jeebies
• give someone their due
• give someone their head
• give someone their marching orders
• give someone their walking papers
• give someone the jitters
• give someone the kiss of life
• give someone the nod
• give someone the old heave ho
• give someone the once-over
• give someone the push
• give someone the right of first refusal
• give someone the right to first refusal
• give someone the rough side of tongue
• give someone the rough side of your tongue