Wanker literally means "one who wanks" (masturbates).
It is normally intended as a general insult rather than as an accusation.
Wanker has similar meanings and overtones, to American pejoratives like "jerk",[1] "jerk-off", and "prick".
One particular connotation is of someone self-obsessed or a show-off (usually male)
In Australia the word has developed a metaphorical usage, in which to wank or to be a wanker implies egotistical and self-indulgent behaviour. This meaning is used in phrases like smug wanker, egotistical wanker or pretentious wanker.[5] Wanker is sometimes used to refer to a person in the same way as snob for subjects perceived as pretentious; for instance, wine wanker, fashion wanker, car wanker.[6]
http://en.wikipedia.org/wiki/Wanker
I have put the full URL in because "wiki wanker" amuses me.
Wiki wanker may well become an A2Kism