Green’s Dictionary of Slang

(Irish) a general excl., euph. for Jesus Christ!

1914		Catholic Bulletin IV n.p.: ‘Oh, Janey Mack, she's mad,’ said Custhard-Puss.
1922		Joyce Ulysses 11: Have you a key? a voice asked. / — Dedalus has it, Buck Mulligan said. Janey Mack, I’m choked.
1939		‘Flann O’Brien’ At Swim-Two-Birds 104: By Janey he’d be up at the whistle with a pome a yard long.
1950		S. Murphy Stone Mad (1966) 54: ‘Be the janey,’ said Stun.
1956		J. Curtis Look Long Upon a Monkey 85: Janeymac, I’m sorry for that.
1963		L. Daiken Out Goes She 39: Janey Mac, me shirt is black / What’ll I do for Sunday?
1969		T. Murphy Crucial Week in the Life of a Grocer’s Assistant (1978) Scene xi: Bejaney-mack-tonight, I said to myself, get it out of here lively.
1973		H. Leonard Da (1981) Act I: Oh, Jancy, I think I’ll go mad.
1981		(con. c.1920) P. Crosbie Your Dinner’s Poured Out! 61: Janey, he gev me the very same.
1982		(con. 1930s–50s) E. Mac Thomáis Janey Mack, Me Shirt is Black 34: Janey Mack he scalped you.
1985		T. Murphy Conversations on a Homecoming (1986) 30: Bejaneymack tonight, you’re looking smashing!
1987		(con. 1930s) L. Redmond Emerald Square 145: ‘Janey Mac!’ said Bay. ‘The bushes are drippin’ with berries.’.
1990		R. Doyle Snapper 30: Ah janey.
1995		A. Higgins Donkey’s Years 20: Ah be Janey Mack, give over!
1995		P. O’Keeffe Down Cobbled Streets, A Liberties Childhood 45: Janey mac, I thought they were all bald!
2001		G. Coughlan Everyday Eng. and Sl. 🌐 Janey Mack! (exclam): Gosh, really?
2010		C. Oliver Laying the ghost 112: Janey Mack, I forgot, I’m on the patch.