Green’s Dictionary of Slang

1. (orig. US) an important person; usu. in negative, an arrogant, self-opinionated person [shit n. (2a)].

1945		in T. Shibutani Derelicts of Company K (1978) 267: Well, those guys are used to being King Shit, that’s why. Over there the instructor yells, and everybody snaps shit.
1967		P. Thomas Down These Mean Streets (1970) 39: I could walk that mean street and not get hurt; I was king shit and bottle washer.
1971		B. Malamud Tenants (1972) 33: Man, if I had that amount of bread I’d be king of Shit Mountain.
1978		R. Price Ladies’ Man (1985) 50: Fucking Al might have been King Shit when it came to sales.
1978		S. King Stand (1990) 1163: Making him feel as if he was [...] King Shit of Turd Mountain.
1997		T. Fontana ‘A Game of Checkers’ Oz ser. 1 ep. 8 [TV script] Watch your mouth McManus. You ain’t king shit around here no more.
2001		J. Stahl Plainclothes Naked (2002) 273: Guy may be King Shit inside, out on the street he’s just another psycho with artillery.
2005		A. Lovejoy Acid Alex 225: I stood blinking before a Jakkalskop Captain. [...] King shit among the dick-yo-nuts in the electric-firebucket brigade.
2023		(con. 1962) J. Ellroy Enchanters 132: I breezed in like King Shit.

2. a major drug dealer [shit n. (5)].

1997

(con. 1960s) A. Frewin London Blues 197: Sonny [...] looking like a super pimp from harlem (or, failing that, King Shit, the mythical reefer dealer all young black hoods aspire to be).