Literally, wanker is accepted to mean "one who masturbates". The frequency of masturbation required to confer the status of "wanker" upon an individual is open to interpretation, as the insult is used as a catch-all category to include fools, buffoons, idiots etc. They're all wankers - the lot of 'em. The cop who caught you speeding, the politician you just saw on TV, those insipid tossbags moaning about global warming. All wankers.
Rarely, the word is used by some to refer to the penis itself, though this usage doesn't seem to be widely known.
"Paul is such a wanker - he killed a toddler while driving drunk. He's due in court on Tuesday."
"Which one of you wankers ate my schnitzel?"
"Drop your wankers and get over here, I need a hand with this..."
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