When someone, or a group, acts as though they are doing something amazing, or phenomenal, or "really meaningful" or important, when to everyone else they are just humiliating themselves.
Based on the characters in the movie, "Waiting for Guffman," or any of Christopher Guest's ensemble films.
My biggest Guffman Moment was in high school when I auditioned to be one of the male cheerleaders, while wearing a self-designed costume with puffy sleeves and gold lame' short shorts. At my 20th reunion, they were still teasing me about it.
At some point George Bush is going to realize that his whole life was a Guffman Moment.
An individual who spouts utter bollocks all day long, but does it in a way that's marginally funny. They generally have no idea that they are full of shit. They're just stupid.
Ruler of Lake Titicaca. Rumored to have a bunghole that gets very angry if it does not receive toilet paper. Cornholio the Great is often seen walking around with his shirt over his head and his hands in the air, chanting songs about his power, and his bunghole.
"I am Cornholio! You do not want to face the wrath of my bunghole, for I need TP!"
Butthead: Shut up, Beavis! (uh huh huh huh)
Beavis: Um, okay. (heh heh heh heh).