The Collaborative International Dictionary of English v.0.48:

bare-ass \bare-ass\ (b[^a]r"[a^]s`), bare-assed \bare-assed\
   (b[^a]r"[a^]st`),adj.
   completely naked. [informal]

   Syn: in the altogether, in the buff, in the raw, raw, peeled,
        naked as a jaybird, stark naked.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bare-ass
    adj 1: (used informally) completely unclothed [syn: bare-
           assed, bare-ass, in the altogether, in the buff,
           in the raw, raw, peeled, naked as a jaybird,
           stark naked]