in the buff vs bare-assed

in the buff and bare-assed both are adjectives.

Word	Noun	Adjective	Verb	Adverb
in the buff	No	Yes	No	No
bare-assed	No	Yes	No	No

As adjectives, in the buff and bare-assed are synonyms defined as:

Other synonyms of in the buff include bare-ass, in the altogether, in the raw, naked as a jaybird, peeled, raw, stark naked.

in the buff (adjective)	bare-assed (adjective)
(used informally) completely unclothed	(used informally) completely unclothed