The rock on sign upside down. Given as a rude gesture to mostly people wearing Slipknot shirts, and shirts of other gay Metal bands. It is basically saying the opposite of "Rock on".
I saw this kid at the mall in a Slipknot shirt, and I gave him the upside down rock on sign. Then he ran away and cried.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi