Top Definition
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!"
by zandwich October 05, 2010
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