barroom genius

Someone who has the gift of bull****. Usually is the one at the bar that pretends to be an expert on a subject after reading one newspaper article on it. Usually is thought of as a "genius" by the surrounding drunks, who don't know any better.

John: Hey, did you hear what Sam had to say on that subject last night at the bar??

Mike: Are you kidding? That idiot is a barroom genius. The only people dazzled by him are the drunk fools that don't know any better.