Green’s Dictionary of Slang

(Can./US) stark naked.

1958		L.F. Cooley Run For Home (1959) 138: I see this miserable shit, balls-ass naked, hanging by his hands from an overhead beam.
1978		R. Caron Go-Boy! 154: The two rascals disappeared [...] emerging a moment later balls naked.
1978		P. Hamill Dirty Laundry 60: There is a pervert right outside your station house, Nolan. Balls-ass naked.