Green’s Dictionary of Slang

tough, ruthless.

1936		W.J. Blackledge Legion of Marching Madmen 13: He may have been a tough, hard-case wallah, but he usually managed to keep a cool head.
1940		F. Sargeson ‘A Pair of Socks’ A Man and His Wife (1944) 64: As for Bill, he was the hardest case bloke you ever came across.
1947		W.D. Overholser Buckaroo’s Code (1948) 52: You’ve got a hard-case rep, but you’re plumb yellow.
1954		H.W. Edwards Under Four Flags 79: They may be ‘hard case’ officers, but they know their jobs.
1960		N. Hilliard Maori Girl 127: All they get there is Pommies off ships [...] and hard-case dames, and jokers who don’t know what to do with themselves.
1974		(con. 1930s) I. Agnew Loner 67: A hard-case bastard, that Whippet.
1986		C. Stroud Close Pursuit (1988) 2: I look a bit like a plain-clothes cop [...] a little on the beefy side, hard-case moustache.
1999		Guardian Guide 6–12 Nov. 4: Carter and Regan were hard-case coppers who hated the system.
2002		J. Lerner You Got Nothing Coming 46: I’m talking about a hardcase fucking joint! [...] got fucking walls five hundred feet high.
2019		S.M. Jones Lives Laid Away [ebook] ‘Just stop all this hard-case bullshit, awright?’.