Green’s Dictionary of Slang

skunk adj.

(US) second-rate, inferior.

1940		E. Hemingway letter 4/11 Feb. in Baker Sel. Letters (1981) 502: He thinks I am skunk brave and have no brains.
1943		W. Guthrie Bound for Glory (1969) 355: You’re a sneakin’ fifth column sonofabitch! Tryin’ ta pertect them skunk Japs.
1969		‘Iceberg Slim’ Pimp 178: Reefer is for low-class skunk broads.
1979		‘Iceberg Slim’ Airtight Willie and Me 10: You ain’t nothing but a foxy dude to stop playing for skunk bitches.
2000		F.X. Toole Rope Burns 42: Germans have us freezing cold in some skunk hotel smell of piss and beer.
2011		F. Bill ‘Beautiful Even in Death’ in Crimes in Southern Indiana [ebook] Fenton had tossed down a few skunk beers he’d hidden beneath his seat.

In derivatives

skunky (adj.)

(Aus.) duplicitous, reprehensible.

1894

Truth (Sydney) 11 Mar. 4/2: In much the same skunkly schedule may be graded every crime known to humbug and artifice, and pricked out in topsy-turvy defintions by Parliament.