Green’s Dictionary of Slang

(Aus., Melbourne) a drink based on methylated spirits with some form of mixer to mediate the taste.

1931		Register News-Pictorial (Adelaide) 6 Feb. 8/3: According to a statement [...] at the Fitzroy court today, the Fitzroy ‘cocktail’ [...] is compounded of kola beer and methylated spirits.
1935		Mirror (Perth) 20 July 2/2: His mother found a partly consumed bottle of drink in his overcoat pocket. The boy told her that it contained a ‘Fitzroy cocktail.’ She took the bottle along to a chemist, and he found that it contained port, plonk and metho.
1946		Cairns Post (Qld) 15 Jan. 7/5: Methylated spirits, ginger beer and a teaspoon of boot polish. In dead-beat parlance this is called a Fitzroy Cocktail or a Domain Cocktail.
2002		Highland Way (Tallong, NSW) Online 30 Nov. 🌐 Fitzroy Cocktail – this uses metho, ginger beer and a teaspoon of boot polish, no wonder everyone had dirty boots.