billyache
What your get BUTT eventually develops from being repeatedly BUTTED by one or more male members of da "best BUTTER in America" species.
It's said dat goats aren't actually born with a strong urge to use their scalps as battering-rams for your posterior; it's a learned trait from having humans playfully pat or push on their heads when they're small. So simply refrain from such "encouragement to engage" behavior if you don't want major billyaches later on.