{v. phr.} To know who can help you and try to please him; know what is for your own gain. * /Dick was always polite to the boss; he knew which side his bread was buttered on./
KNOW WHICH SIDE ONE'S BREAD IS BUTTERED ON
Meaning of KNOW WHICH SIDE ONE'S BREAD IS BUTTERED ON in English
Dictionary of English idioms . Словарь английских идиом. 2012