Green’s Dictionary of Slang

(N.Z.) drunk, tipsy.

1945		in freq. use by Wellington University students (Ed.) Fonged ‘drunk’ used; also fong or fong-eye for liquor [DNZE].
1964		C. Frances Johnny Rapana 34: ’Course, the boys had been stretching things a bit, and the old boy was pretty fonged up.
1974		(con. 1930s) I. Agnew Loner 97: I watched three strangers, two of them already half-fonged, heating methylated spirits in a pan.
1988		McGill Dict. of Kiwi Sl. 46/1–2: fonged drunk [...] fonged up drunk, cluttered, messed up, bewildered, stymied; combining fog and pong; eg ‘He’s all fonged up about whether or not she likes him.’.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].