Green’s Dictionary of Slang

cheap, inferior; in poor taste, e.g. a schlock movie.

1916		Marketing Communications 96 102/1: Some of the biggest dry-goods stores have been pilloried, and their methods absolutely changed. Some of the smaller shlock stores have been dissected.
1917		N-Y Trib. 3 June 18/1: Others among the conspicuous local advertisers are of the self-evident ‘schlock’ type.
1939		‘Consumer Vocab.’ in AS XIV:1 80/2: Schlag describes a skirt which has scant length, tightness where it should be full, is off size, has many loose threads, defective buttons, and off size button-holes.
1958		Mad mag. Sept.–Oct. 14: Attention, all you schlock publishers who have never had an original idea in your lives!
1961		H. Ellison Rockabilly (1963) 144: The second-string schlock magazines.
1965		N.Y. Times 4 Feb. 50: The dealers were guilty of schlock, sleazy, bargain-basement, fast-buck advertising.
1970		Harper’s Mag. Dec. 32: Sudden sex and violent death are the two poles of most of the great art, folk art, and shlock art.
1975		A. Goldman Lenny Bruce 15: He‘s got a half-dozen [...] flimsy but elegantly fashionable Continental suits that sell for $49.99 in the Sixth Avenue schlock shops.
1989		M. Amis London Fields 434: He just writes schlock plays and cute journalism.
1990		S. Morgan Homeboy 75: The shlock street characters called shoplifting music.
2000		Observer Screen 9 Jan. 11: Frank Henenlotter’s low-budget, schlock-horror flick.
2021		J. Ellroy Widespread Panic 6: He produced schlockumentaries for islamic TV.