Green’s Dictionary of Slang

(N.Z.) a stomach-ache; lit. and fig.

1941		Baker N.Z. Sl.
1943		J.A.W. Bennett ‘Eng. as it is Spoken in N.Z.’ in AS XVIII:2 Apr. 93: The number of Maori words in common use is comparatively small and tends to decrease as the Maoris become Europeanized [...] puku, stomach, and pukumu, big stomach (used jocularly).
1988		McGill Dict. of Kiwi Sl. 81/2: pain in the puku a bellyache or irritating person.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].