Green’s Dictionary of Slang

1. (US, also hard one) a criminal and/or violent individual.

1872		C.L. Brace Dangerous Classes of NY 111: My dad was a hard ’un. One beautiful day he went on a spree, and he came home and told me where’s yer mother? and I axed him I don’t know, and he clipt me over the head with an iron pot, and knocked me down.
1908		D.G. Phillips Susan Lenox II 141: Terry was a ‘hard one’.
1914		W.Thaw letter 30 Aug. in ‘The War Letters of Two Yale Undergraduates’in Yale Alumni Wkly 22 Jan. 484: There are about 1200 here [...] and in our section [...] there is mixture, including [...] a couple of hard guys from the Gopher Gang of lower N. Y.
1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 27/2: HARD GUY. 1. Prisoner, officer, guard, or anyone else who is unquestionably hard-boiled. 2. Professional criminal or his understudy.
1925		O.O. McIntyre New York Day by Day 20 Dec. [synd. col.] The house policemen are hard guys who are impervious to sympathy.
1932		(con. 1910s) J.T. Farrell Young Lonigan in Studs Lonigan (1936) 22: They were hard guys.
1947		I. Shulman Amboy Dukes 39: Are you supposed to be a hard guy?
1958		R. Chandler Playback 86: Well, well. Mr. Hard Guy in person.
1970		San Diego Sailor 3: It would be easier in the Navy to tag along with the rest of the hard guys.
1973		G.V. Higgins Digger’s Game (1981) 25: I’m up the hundred two hard guys cost me.
1992		G. Wolff ‘At the Fair’ in A Day at the Beach (1992) 115: Here are the hard guys, Billy Badass and his gang.
2000		Wolkin & Keenom Michael Bloomfield 40: Paul was very quiet and defensive and hard-edged. He was this tough Irish Catholic, kind of a hard guy.
2012		C. Stella Rough Riders 62: White investment bankers [...] brokering for Vegas hard guys.

2. attrib. use of sense 1.

1919		H.V. O’Brien diary 20 Jan. in Wine, Women and War (1926) 310: Still playing hard-guy old timer to bunkies.
1950		B. Spicer Blues for the Prince (1989) 141: Lay off the hard-guy stare, Manny.
1995		J. Stahl Permanent Midnight 76: The hard guy thespian’s rigorous personal standards.

3. (US campus) a difficult person.

1986

Eble Campus Sl. Nov. 5: hard guy – a nuisance, a pain to be around.