be on best behaviour

be on your best behaviour

(British & Australian) also be on your best behavior (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.

Common Names:

Name	Pronounced	Usage
Stelios	-	Greek
Lind	[lind]
Aurora	ow-RO-rah (Spanish), ə-RAWR-ə (English), OW-ro-rah (Finnish)	Italian, Spanish, Portuguese, English, German, Romanian, Finnish, Roman Mythology
Golbahar	-	Persian
AthÉNaÏS	a-te-na-EES	French
Hadas	-	Hebrew