Green’s Dictionary of Slang

1. an incompetent, an untrustworthy person; a criminal.

1929		Hostetter & Beesley It’s a Racket! 242: wrong gee [...] one engaged in a racket; professional criminal.
1931		D. Runyon ‘Tobias the Terrible’ in Runyon on Broadway (1954) 112: I will give all you wrong gees a good going-over.
1939		R. Chandler Big Sleep 190: The only time a girl like you goes for a wrong gee is when he’s a handful of mush.
1945		R.L. Bellem ‘Dead Don’t Dream’ in Hollywood Detective July 🌐 They threw the book at him on a habitual-criminal rap: armed robbery, extortion, kidnapping, forgery — hell; he’d been a wrong guy ever since he was a punk in reform school.
1947		S.J. Perelman Westward Ha! 47: I aim to shoot squar’, but if’n you’re a wrong Injun – watch out!
1949		N. Algren Man with the Golden Arm 26: You’re guilty [...] ’cause you’re a wrong guy in a wrong neighborhood out at the wrong hour.
1950		Goldin et al. DAUL 240/1: Wrong ghee. 2. Any non-member of the underworld who is not to be trusted by the underworld; one who may be relied upon to seek police aid on the slightest provocation; a thoroughly law-abiding citizen.
1952		(con. 1948) G. Mandel Flee the Angry Strangers 472: Good riddance, by God – one more wrong guy gone!
1953		R. Chandler Long Good-Bye 234: ‘Why forget it? Let’s open up the wound.’ ‘Suits me. Under the hat, though. To some people you’re a wrong gee. I never knew you to do anything too crooked.’.
1963		B. Hecht Gaily, Gaily 91: Blondie who’s sitting at your table is a wrong guy. Strictly bad news.
1974		G.V. Higgins Cogan’s Trade (1975) 12: Something got fucked up once [...] I picked a wrong guy for something.

2. an informer [spec. use of sense 1].

1949		Monteleone Criminal Sl. (rev. edn).
1950		Goldin et al. DAUL 240/1: Wrong ghee. 1. An informer; anyone who is known to have deviated, however slightly, from the once rigid underworld code.
1991		(con. 1920s) O.D. Brooks Legs 53: They’re afraid a wrong guy might wander downstairs, see what they’re doing and tell the sheriff.
2017		D. Winslow The Force [ebook] ‘[D]oes Carter have someone on the pad?’ ‘Has to be Torres’ Torres is a wrong guy.