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
Chaz	CHAZ	English
Curtis	['kə:tis]
Helias	-	Biblical Latin
Izidor	-	Slovene
Esmeralda	es-me-RAHL-dah (Spanish), esh-mə-RAL-də (Portuguese), ez-mə-RAHL-də (English)	Spanish, Portuguese, English, Literature
Bohumila	-	Czech