Green’s Dictionary of Slang

(Aus.) an alcoholic drink that mixes wine, opium, cayenne pepper and rum, popular at the gold diggings; an alternative recipe mixes boiling water, sugar, lime or lemon juice, porter, rum and brandy.

1853		C.R. Read What I Heard, Saw, and Did 172: The stuff to which I before alluded was called ‘Blow my skull off’.
1972		B. Wannan Folklore of the Aus. Pub 124: Blow-me-skull-off: a name for various heady brews. [...] a popular drink on the Australian goldfields during the 1850s and ’60s.
1999		G. Seal Lingo 133: The problems associated with over-proof and downright dangerous concoctions are also numerous in colloquial speech: [...] blow-me-skull-off; the offensive gin’s piss.