Green’s Dictionary of Slang

(Irish) a generic name for a Dubliner.

1946		D. MacDonagh Happy as Larry n.p.: When one of them dies / He’s burnt to be buried in style; / Right up on the fire will go Jem [BS].
1977		J. Plunkett Coll. Short Stories 42: I’m not offering jembo over there any. He drank enough free whiskey to satisfy a bishop .
1989		H. Leonard Out after Dark 9: What I’m saying is that Jembo here looks like him. Rory could have a cousin, couldn’t he?
1996		Sun. Trib. (Dublin) 9 June n.p.: I was comin home from de pub wit de war department when sez she to me, Jembo, will we buy de papers? [BS].