Green’s Dictionary of Slang

(US) a Mexican-American, esp. a young man who joins a street gang; thus pachuca, his female counterpart.

1943		Himes in Black on Black (1973) 220: Pachuo [sic] is a Mexican expression which originally meant ‘bandit’ but has degenerated by usage into a description of a juvenile delinquent. [...] In Mexican districts in the county of Los Angeles, small bands of pachuos have organized into gangs to fight each other .
1952		Lait & Mortimer USA Confidential 161: Mexican zoot-suiters, known as pachucos, are tough hombres handy with knives, slick-haired pimps and dope-passers.
1966		(con. 1958) R. Farina Been Down So Long (1972) 18: Pachucos in Texas or somewhere. Oeuf told us you were murdered.
1974		R. Stone Dog Soldiers (1976) 106: He was slight and copper-colored, an Indian or a pachuco.
1980		(con. 1940s–60s) H. Huncke ‘Tattooed Woman’ in Eve. Sun Turned Crimson (1980) in Huncke Reader (1998) 115: On one of her hands another tattoo—the sign of the Pachuca.
1986		C. Stroud Close Pursuit (1988) 308: You think he’ll tip the guy? You know, help out another hard-luck pachuco?
1990		S. Morgan Homeboy 50: Day in, day out, goldtoothed pachooks scratching on [the] screen door hissing how they do for cooze.
1993		L. Rodríguez Always Running (1996) 5: This lifestyle originated with the Mexican Pachuco gangs of the 1930s and 1940s, and was later recreated with the Cholos.
2000		J. Ellroy ‘Balls to the Wall’ in Destination: Morgue! (2004) 5: Pachucos lacked heart. They oiled their hair. They overbred. They packed switchblades.
2021		J. Ellroy Widespread Panic 8: Harry has a rancid rep. He stomped two pachucos dead.