The term "filthy casual" is an internet slang used to describe someone who appears to be careless or uninformed about a particular topic, but actually knows quite a bit. Full definition
«Ryan is a daily slayer of filthy casuals with no weaknesses. (relevant-gaming.com)
I've even had to resist the urge to call people filthy casuals because they can't play the game right, something I was called when I couldn't play Dark Souls right. (egmr.net)
@bugsplatreport: Go play Angry Birds you filthy casual! (gamespot.com)