Green’s Dictionary of Slang

(Irish) a fool.

1827		Finn’s Leinster Jrnl (Kilkenny) 8 Sept. 1/2: Sure, you bosthoon, if I’m ugly myself [...] the girls don’t say so.
1833		W. Carleton Traits and Stories of Irish Peasantry I 328: Why, you great big bosthoon.
1842		S. Lover Handy Andy 322: You dirty bosthoon.
1851		Bell’s Life in Sydney 15 Mar. 3/1: You bosthoon, / Sure the heathens can’t drink with the Christians.
1861		Kerry Eve. Post (Tralee) 19 June 2/2: The blundering inconsistency of the over-grown bosthoon who thus knocks with this impertinence at the palace gate.
1870		Gympie Times (Qld) 23 Mar. 3/3: I confess I am ignorant of the true or the slang moaning of the word ‘bastoon’.
1872		Irish Examiner (Cork) 12 Dec. 3: The defendant was a poor bosthoon of a farmer [...] drunk morning, noon and night.
1879		H. Hartigan Stray Leaves (2nd ser.) 4: Doyle [...] belonged bonâ fide to the Fut Artillery—but he averred that he ‘was only lent to them to tache the bosthoons the new gun drill!’.
1884		Nation (Dublin) 28 Apr. 8/1: A more ignorant and low-minded set of bosthoons cannot be found in the civilised world.
1893		F.P. Dunne in Schaaf Mr Dooley’s Chicago (1977) 77: What d’ye think th’ poor bosthoon replies?
1898		Regiment 25 June 197/3: ‘There’s one for Ireland’s eye, you ugly looking bosthoon,’ and Pat landed the coloured soldier one in the right peeper.
1904		G.B. Shaw John Bull’s Other Island II ii: You bosthoon, you!
1914		Joyce ‘Grace’ Dubliners (1956) 158: Is this what we pay rates for? [...] To feed and clothe these ignorant bostooms.
1923		Eve. Herald (Dublin) 7 Apr. 7/6: I’d lay you tens that the horse had more brains than the bosthoon that’d been whipping it.
1932		S. Beckett Dream of Fair to Middling Women (1993) 53: On two counts, subsequently, by the Civic Guards, those plush boshoons, they were indicted: breach of turbary and cruelty to the ass.
1942		E. Cross Tailor and Ansty 178: A great stupid block of a bosthoon of a fellow? A proper galoot, if ever a galoot walked the face of this earth?
1952		B. MacMahon Children of the Rainbow 13: You base-bred bostoon!
1968		(con. 1940s) J. Healy Death of an Irish Town 26: The ‘ignorant bosthoon of a spalpeen’ who told you ‘put your money where your mouth is’ in too many arguments.
1977		Connacht Trib. 1 July 9/7: You described him as a ‘Yahoo’ but seeing that he aspires to being a Gael, then I feel that the more correct title for hime is ‘Bosthoon’ .
1987		Irish Farmers Journal 11 July 9/4: All they'd require is a few operating sheds for repairs and an odd ignorant bosthoon of a surgeon with a good pair o' hands on him.