The bible talks about the shepherd separating the sheep from the goats Math 25: 31-46. Obviously the sheep are good and goats are not. So if they got his goat...then his bad evil sinful side is coming out. Perhaps not a creative enough answer but may be a truthful one as to the origin.
I like that explanation! And the Bible also talks about "scapegoat", but that's a little too deep for me.
You get the first big upvote!