know which side one's bread is buttered on

Verb

 * 1)  To be aware of where one's interests lie in a situation.
 * , Episode 16:
 * He knows which side his bread is buttered on though in all probability he never realised what it is to be without regular meals.
 * , Episode 16:
 * He knows which side his bread is buttered on though in all probability he never realised what it is to be without regular meals.