What is the meaning of ‘duh’?

First, let’s deal with the pronunciation of this word. The ‘u’ is like the ‘u’ in ‘cut’ and ‘but’ and the final ‘h’ is silent. When someone says something, and you respond by saying ‘duh’, you are telling the person that what he has just said is obvious. You are being sarcastic. It’s your way of saying, ‘tell me something I don’t know’. The word, which is considered slang, is frequently used in informal contexts in American English.

Do you know that Ramesh and Sujatha are planning to get married?

Duh!

“Never accept a drink from a urologist.” — Erma Bombeck