Green’s Dictionary of Slang

1. cheap alcohol; spec. cheap red wine.

1902		DT 20 June ii I: He explained his action by saying that he was in lunatic’s broth – otherwise drunk – at the time [F&H].
1941		Baker Popular Dict. Aus. Sl. 45: Lunatic soup, cheap red wine.
1943		M. Harrison Reported Safe Arrival 125: I must have a taste of decent liquor. Or even a bottle of Red Biddy. Lunatic’s Broth.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxvi 4/1: lunatic soup: Booze of any description.
1981		S. McAughtry Belfast 6: My job’s to keep the cutomers supplied with lunatic broth.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 15: His acting the purse man brought the place to life. The bots ordered up only the best brands of lunatic soup from the top shelf.
1986		R. Beckett Dinkum Aussie Dict. 35: Lunatic soup: Alcohol in any form.
2016		N. Cummins Adventures of the Honey Badger [ebook] I was pretty stoked and nervous, with all of my long-lost relations making the game, and half full of lunatic soup.

2. (also electric soup) methylated spirits as drunk by alcoholics.

1946		D. MacDonagh Happy as Larry Act IV: Was it brandy I drank on top of whiskey, / Or poteen brewed from Connachtmen’s socks, / Or Lunatic Soup or American hooch.
1950		P. Hoskins No Hiding Place! 191/1: Lunatics’ Broth. Red biddy (wine adulterated with methylated spirit).
1981		S. McAughtry Belfast 146: The cops knew him as harmless: just too fond of the electric soup.
1988		McGill Dict. of Kiwi Sl. 70/2: lunatic soup alcoholic drink, including meths (methylated spirits).
1993		(con. 1930s) M. Verdon Shawlies, Echo Boys, the Marsh and the Lanes 62: In those days some of the men went on benders. They’d go mad for the drink, absolutely mad [...] Some – not many – but some would even drink methylated spirits. They would. ‘Lunatic soup’, we called it.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].