peanut butter

bread and butter

That which is central or fundamental, as to one's business, survival, or income; a staple or cornerstone.

butter face

Alternative form of butterface.

butter one's bread on both sides

To profit from two things at the same time, especially when those things seem contradictory or incompatible.

butter the cony

To take advantage of an unmissable opportunity.

butter wouldn't melt in someone's mouth

The identified person appears to be benign, mild-mannered, or calm (but with an integral suggestion that, to the contrary, they really are untrustworthy, disagreeable, or mean-spirited).

like butter on a bald monkey

Very smooth.

peanut gallery

Any source of heckling, unwelcome commentary or criticism, especially from a know-it-all or of an inexpert nature. May also now refer to general audience response: "Let's hear it from the peanut gallery."

put butter on one's bread

To earn money.