I think the "You're a fcuking cnut!" bit towards Whistle Blower might have had a helping hand. I mean, we all think it of the tosser but, jeez, you've got to keep it to yourself.
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Take the piss (out of someone) vb. British -- to mock, deride, poke fun (at). This vulgarism has been in widespread use since the late 1940s. The original idea evoked by the expression was that of deflating someone, recalling the description of a self-important blusterer as 'all piss and wind.'