know which side one's bread is buttered on

verb1

•
To be aware of where one's interests lie in a situation.
- He knows which side his bread is buttered on through in all probability he never realised what it is to be without regular meals. — 1922

forms

knew which side one's bread is buttered on · knew which side one's bread was buttered on · known which side one's bread is buttered on · known which side one's bread was buttered on · knowing which side one's bread is buttered on · knows which side one's bread is buttered on