prunes and prisms
Intentionally formal or prudish speech or action. The phrase originated in Charles Dickens' novel Little Dorrit as an example of proper speech. When you talk to your grandmother, stick to prunes and prisms so that you don't offend her. If you want to become a proper lady, be sure to practice your prunes and prisms.
prunes and prisms
used to denote a prim and affected speech, look, or manner. In Charles Dickens's Little Dorrit ( 1857 ), Mrs General advocates speaking this phrase aloud in order to give ‘a pretty form to the lips’.