When he says it's an inside joke, it's not a stripcreator forum inside joke... it's an underground metal inside joke.
Despite the fact that I'm no stranger to metal, I'm at a loss as to what the joke here is, aside from perhaps that the various backgrounds are references to death metal bands, and the guy in the trashcan is a metalhead who hates radio-metal.
Don't even ask me what's up with the squirel.