The more
popular term derived from buck naked.
some
people still say buck naked, but most say
butt naked because the yanks made a cooler version of the term.
Johnny: "Haha, I just saw your girlfriend
butt naked"
John Henry Smith III: "You stupid American, it's "buck naked"! Bloody twit!
Johnny: "Haha, Yeah, but we are more
popular, and our term is better, so we win by default. Either way, I still saw your
girlfriend naked."