The day you beat me, pigs'll fly out my ass
A.K.A. it’s never gonna happen
This picture fits the lyrics if we take a brief stop here (as Em' does in his delivery), it is however misleading as the rest of the bar depicts the pigs to be in sausage form, and that the flying mean is by a flying saucer.
Could also be keeping with the football idea, since a football is also referred to as being a pig skin.
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