A double poser is someone who looks like a poser from some stupid counterculture, but in fact knows nothing about the music or customs of that specified subculture. In effect they are posing like they are a certain kind of a poser, but are even lamer and to ignorant to even be taken seriously by anyone. These people are very common in the Indie Rock and punk scenes, but are occasionally also on the fringes of the metal "scene" as well. A wannabe's wannabe.
"Man that stupid douche bag with a spiked belt and mohawk didn't even know who GBH is...He probably listens to Blond Redhead and cries himself to sleep every night. What a double poser!"