Green’s Dictionary of Slang

(Irish) any person, with rebellious even villainous overtones (see cites 2017), also as an affectionate term of address.

1940		S. Longstreet Decade 317: Cokey too, this shamos, and ready to kill on any beef.
1953		B. Behan Scarperer (1966) 11: All the shams, they put in threepence of a night with Pig’s Eye O’Donnell.
1968		(con. 1930s) J. Healy Death of an Irish Town 20: They were, in the current slang of the town, ‘the buff shams’.
1985		T. Murphy Conversations on a Homecoming (1986) 54: No bother there, sham.
1999		D. Healy Sudden Times 14: Hi Sham, he says.
2001		G. Coughlan Everyday Eng. and Sl. 🌐 Sham (n): used by a man from a rural area when addressing one from the city e.g. How’s it goin’, sham?
2017		L. McInerney Blood Miracles 8: Half of Ireland will want in on it. The Shades and the shams, all looking for a cut [of drug dealing].
2017		L. McInerney Blood Miracles : The two oldest Cusack boys, a right pair of shams-in training, you’d want to givem a wide berth.
2021		L. McInerney Rules of Revelation 52: ‘Happened to a sham I used to pull pints with in Galway. He broke his hand in a fight’.