say a mouthful
Utter something important or meaningful, as in You said a mouthful when you called him a fine musician. This term is often used to express agreement, much as you can say that again is. It was first recorded in 1790.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.