Green’s Dictionary of Slang

used of a cheap version of an originally expensive garment.

1999		J. Ridley Love Is a Racket 29: I turned to her and got a faceful of some cheap knockoff Rolex.
2001		G. Pelecanos Right As Rain 217: The man wore thick glasses with black frames and a knockoff designer sport jacket.
2012		(con. 1980s) I. Welsh Skagboys 44: He usually wears expensive italian shoes, always knock-off.
2020		S.A. Crosby Blacktop Wasteland 249: ‘Daddy [...] bought me that knockoff G.I. Joe action figure’.