Literally '
One who wanks' (masturbates)
Used derogatively to infer
one who is unable to get any and relieve their need to wank due to gross personality defects.
Australian (and particularly Melburnian) usage infers
one who is a pseudo-intellectual or more generally speaking out of their arseholes in an effort to impress.
See also: Tosser, Tosspot, Pillock, jerk, arsehole, wanka, wank.