Goose Arse

A negative description of an individual who's entire arse sticks out from the body while they stay in an upright posture. This is caused by the individual pushing their lower back and hips backwards on a constant day-to-day routine and over years of holding this posture causes what we now call a goose arse, because they waddle around with their arse stuck out.
A prime example of this 'Goose Arse' effect would be the character Lechero from Prison Break season 3, the prison boss.

John: ..hey! Get aload of goose arse over there.
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Ben: What's up with this guy?
Mark: That's Ol' McGoose Arse mate
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Gaz: Argh! Tony's p*ssin' me off.. he doesn't do any work round here.. all he does is boss us around while he just sits on his fat f*ckin' goose arse.