I've already blogged about D'Oh (twice) and the first time I did so I mentioned it was not to be confused with Duh. Duh (pronounced duhhrrr) is an American English slang exclamation that is used to express disdain for someone missing the obviousness of something. It can also be used when someone states the obvious.
I cannot think of a better example of the appropriateness of "Duh!".
The Empire Inn Sign
7 hours ago