Green’s Dictionary of Slang

1. Johnny Walker whisky; differentiated as Johnny Red, Johnny Black, denoting labels/strength.

1957		D. Niland Call Me When the Cross Turns Over (1958) 34: I’m coming along to see you with half a bottle of Johnny.
1970		G. Scott-Heron Vulture (1996) 8: Now I sat in a fabulous crib drinking Johnny Black.
1981		G.V. Higgins Rat on Fire (1982) 62: ‘Suppose you want a drink to go with it.’ ‘Johnny Red and soda.’.
1985		B. Humphries Traveller’s Tool 34: The bottle of Johnny […] hits the deck and explodes.
1997		Share Slanguage.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 383: Barb popped pills. Barb popped Johnnie Black.
2012		R. Brunet ‘Lucky for Me’ in ThugLit Dec. [ebook] [O]rdering a pair of double Johnnie Reds.
2022		I. Fitzgerald Dirtbag, Massachusetts 97: Three Wise Men [...] A single huge shot glass, which had three regular-sized shots poured into it: Jack, Jim, and Johnnie.

2. see John n. (4)