Green’s Dictionary of Slang

John B n.2

also john bum
[John- pfx + bum n.3 (2)]

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El Paso Times (TX) 28 July n.p.: ‘The minute you made the motion, you were sized up by John Bum as a ’mark.’ Not only does John Bum know when to touch a mark, he knows where to find the mark [...] I have never seen a John B whether in the jungle or on the stem who wasn’t a drunk or drug addict.