Green’s Dictionary of Slang

1. strong liquor.

1939–45		Expressions and Sayings 2NZEF (Nat. Archiv. TS WAIL DA 420/1) Fong-Fong-eye. Liquor of a dubious nature [DNZE].
1967		F.W. Miller Ink on my Fingers 177: The ‘fong’ experts were not encouraged by the genuine talent and were usually avoided [DNZE].
1979		Gebbie & Mcgregor Incredible 8-Ounce Dream 89: A group of regular drinkers set up a kitty to pay for taxis home [...] One of the farsighted drinkers threw a dollar to the ‘fong fund’ and made the comment, ‘Tell me I’m not fit to drive and I’ll use that to get a taxi home.’ [DNZE].
1985		Metro (Auckland) Sept. 47: On the odd occasion he wouldn’t front up in the morning. I always assumed it was because he’d attacked the fong (booze) the night before [DNZE].
2003		McGill Reed Dict. of N.Z. Sl. 81: fong Booze.

2. methylated spirits as drunk by alcoholics.

1974		(con. 1930s) I. Agnew Loner 39: It was so much easier to pay sixpence for a bottle of methylated spirits, commonly referred to as fong, drown your sorrows and lose yourself in a world of fantasy.
1988		McGill Dict. of Kiwi Sl. 46/1: fong methylated spirits.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].

3. a very heavy drinker.

1968

G. Slatter Pagan Game (1969) 174: They stopped for a leak on the Wakatahuri Hill and Fong Needham fell down the bank.