A combination of bare assed and buck naked. Another form is
buck ass nekkid. Usually applies to a
drunk frat boy types in
innocent homo-erotic situations while hard drinking with their buddies.
Josh: "Hey, that Chad guy is
buck ass naked and sportin' a semi."
Jake: "Yep, he's a nudie."
Jeremy: (as he drops his boxers) "Yeah, he'll nude up any
time, anywhere."