It's when a person fails to do something or says something that just doesn't work. When the result of something is totally unsatisfactory and/or potentially embarrassing.
It's like when a cake tastes like a dry piece of cornbread with super sugary icing on top: basically unpalatable.
Person 1: Did you see that guytrip over his pant leg just now?
Person 2: Yeah, that was a total fail cake. Sucks to be him.
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).