Green’s Dictionary of Slang

a general intensifier.

1897		E.W. Townsend Chimmie Fadden 7: Say, if I didn’t come near getting de grand bounce, de straight turn out, me name’s not Chimmie Fadden.
1976		R. Price Blood Brothers 17: I ain’t never gonna live here. I live in fuckin’ Co-op City an’ that’s straight life.
1991		L. Bing Do or Die (1992) x: When I was younger I was a straight killer.
2019		N. Walker Cherry 107: Your wife’s a no-good straight piece-of-trash whore.