Green’s Dictionary of Slang

(Aus./US) an emphatic ‘no!’.

1901		Independent (Honolulu, HI) 3 July 2/1: The Colonel’s answer was ‘Nitsky’.
1906		C. M’Govern Sarjint Larry an’ Frinds 12: You would clasp de stranger to your bosom and wep on his neck [...] Of course you would! Auber nitski!
1911		S.F. Call 19 Mar. 9/3: ‘Did the old man [...] offer to shake hands?’ ‘Nitsky!’.
1915		Truth (Brisbane) 25 July 3/3: ‘[I]t’s nitzey on the C.I. guns to me’.
1917		A. Conan Doyle His Last Bow in Baring-Gould (1968) II 799: The gunner turned durned nasty at the last, and I had to square him with an extra hundred dollars or it would have been nitsky for you and me.