Green’s Dictionary of Slang

(orig. Irish) a would-be gentleman who puts on superior airs; orig. an Irish person aping the English gentry.

1907		Lone Hand (Sydney) June 191/2: This [Roman Catholic] paper has two favored words of reproach for persons who do not come up to its standards of furious sectarianism. They are ‘shoneens’ or ‘Englishmen’.
1909		‘The Lang. of Crooks’ in Wash. Post 20 June 4/1: [paraphrasing J. Sullivan] A shoneen is an Irish upstart.
1914		Joyce ‘Ivy Day in the Committee Room’ Dubliners (1956) 119: Hasn’t the working-man as good a right to be in the Corporation as anyone else – ay, and a better right than those shoneens that are always hat in hand before any fellow with a handle to his name?
1922		Joyce Ulysses 297: So then the citizen begins talking about the Irish language and the corporation meeting and all to that and the shoneens that can’t speak their own language and Joe chipping in.
1939		N. Algren ‘Lightless Room’ in Entrapment (2009) 45: Then [he’d] call O’Connor a underfed shoneen.
1947		N. Algren Neon Wilderness (1986) 154: You might not think no husky little Irish blondie like me could get scared of an underfed little shoneen like that.
1986		J.B. Keane Bodhrán Makers 181: ‘Have you any more Irish?’ Katie asked. ‘Hardly any I’m sorry to say [...] It was swept from us by time and by the shoneen and the foreigner.’.
1995		Irish Times 25 Sept. n.p.: While some ‘Dubs’ consider provincials less than the full civilised shilling – ‘muck-savages’ is a phrase which comes to mind – some provincials appear to consider Dubliners less than fully Irish: ‘Jackeen’ in its etymology is a form of ‘Shoneen’, a sort of working-class ‘West Brit’ [BS].