A higher degree of insult than plain old 'wanker'. Usually used when someone has done something incredibly foolish whilst someone was watching. Pronounced normally with a sarcastic inflection to maximise effect.
Two people are playing CoD MW2 and one of them is owned by his own grenade
Guy 1: OMG I just blew my self up with my Semtex!!!
Guy 2: Muwah ha ha! Fucking wankerchank!
Guy 1: Screw you man...