Wiktionary
no duh
alt. (context chiefly US colloquial sarcastic English) (non-gloss definition: An expression or exclamation that something is exceedingly obvious or apparent, or that one would have to be extremely foolish not to realize something immediately.) (From 1962.) interj. (context chiefly US colloquial sarcastic English) (non-gloss definition: An expression or exclamation that something is exceedingly obvious or apparent, or that one would have to be extremely foolish not to realize something immediately.) (From 1962.)