Green’s Dictionary of Slang

(US) it is of no importance to me, ‘I should worry’.

1913		T.A. Dorgan in Zwilling TAD Lex. (1993) 49: Ish ki bibbel.
1914		Goodwin’s Wkly (Salt lake City) 14 Mar. 9/3: [advt] Ishkabibble! Mother has a new gas range [...] I don’t have to carry no more coal.
1917		Tacoma Times (WA) 30 Aug. 3/6: ponderous London dailies are perturbed over ‘Ish Kabibble.’ One solemnly hazards it means ‘What’s the odds’.
1925		Dos Passos Manhattan Transfer 215: Gosh I’m an indecent sight in this dress . . . . Ish gebibble.
1926		C. Ryan ‘From “Quoz” to “Razzberries”’ in AS II:2 92: We next read on the sport’s arm ban and the flapper’s pennant ‘Ish Kabibbul’ or ‘Ishkabibble’ — or ‘I Should Worry’.
1929		T. Wolfe Look Homeward, Angel (1930) 360: They [i.e. summer houses] were small, flimsy, a multitudinous vermin — all with their little wooden sign of lodging. ‘The Ishkabibble,’ ‘Sea View’, ‘Rest Haven’.
1933		J.T. Farrell Gas-House McGinty 358: You should worry. Ish kabbible, Mac.