Green’s Dictionary of Slang

(orig. US) excellent, best.

1920		Collier’s 20 Mar. 35/3: All you could see was her little peaches and grade A cream face stickin’ out over the top .
1934		S. Walker City Editor 37: The ordinary American newspaper reporter [...] was regarded as essentially a wastrel and, given the opportunity, a Grade-A guttersnipe.
1942		N. Algren Never Come Morning (1988) 174: Even after all the years I been runnin’ a grade-A re-fined house.
1953		J. Thompson Alcoholics (1993) 122: A grade-A nut.
1959		A. Anderson ‘A Sound of Screaming’ in Lover Man 44: We’d get high and have us an A-grade ball.
1960		C. Cooper Jr Scene (1996) 157: And I like livin like this, man, ’cause it’s pure, like grade-A boy!
1978		L. Kramer Faggots 287: Being confronted by so much Grade A male flesh, most of which seemed superior to his.
1984		(con. 1976) B. Simon ‘Black Dog’ Born in the RSA (1997) 26: My mother-in-law is a Grade A bitch.
1989		T. Blacker Fixx 170: An irresistible Grade A pistol between the sheets.
2000		L. Howard All the Queen’s Men 319: She would have to be a Grade A fool to love John Medina.
2012		J. Díaz This Is How You Lose Her 20: At least Rupert gives me some Grade A dick.
2016		T. Robinson Rough Trade [ebook] [T]he guy was a Grade-A asshole.