An exclamation you make when you realize something you should have known all along, or when the person you're with has a startling revelation about something obvious.
Bob: "Wow! I never knew that donuts were so bad for you!"
Sally: "Duh 101"
Francine: "I should have known he was married! Duh 101!"
Sally: "Duh 101"
Francine: "I should have known he was married! Duh 101!"
by zandwich October 5, 2010