Green’s Dictionary of Slang

1. intensifying extension of black, pertaining to colour or race [-ass sfx].

1961		R. Gover One Hundred Dollar Misunderstanding 125: See, Madam, she got this great big ol blackass car.
1973		D. Goines Street Players 81: You dirty, black-ass bitch, you!
1997		Simon & Burns Corner (1998) 116: Why, they asked Tyreeka, did you pick that ugly, black-ass nigger?

2. as a negative intensifier [-ass sfx].

1971

B. Malamud Tenants (1972) 69: What a blackass fool I was to let you read my book.

3. melancholy, depressed [black ass n.].

1974

(con. 1940s) E. Thompson Tattoo (1977) 237: Buck went deeper into a blackass sulk.