When someone doesn't know the answer to a simple question. (Recently, 50% of the Miss USA contestants didn't know who the Vice-President of the USA is.)
"Dude, what time is it?"
"Duh, I don't know, man."
"Thank you, Miss USA."
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi