IIRC, I first encountered the term in a post by merlyn and thought it might be a Randall-ism, perhaps representing an overhead view of two goats butting heads. I've just done a little reasearch and found out that 'butting' is indeed involved: cf. Goatse.cx and goatse if you really gotta know — Update: but first consider the wise counsel of MidLifeXis in Re^4: count repeatation above!

Maybe now I'll look around for a more "right and proper, m'am" alternative! OTOH, does anyone know a link to a 'proper' definition?