Green’s Dictionary of Slang

coachman on the box n.

venereal disease.

a.1945		L. Payne private coll. n.p.: — Coachman on the Box.
1960		J. Franklyn Dict. of Rhy. Sl.
1969		S.T. Kendall Up the Frog.
1978		Maledicta II:1+2 (Summer/Winter) 118: He [...] also lists: [...] Coachman on the Box Pox.
1999		D. Lypchuk ‘A dirty little story’ in eye mag. 8 July 🌐 Thank God he wore a glove or she could be jacked up with a permanent slimming cool, creepers or the dreaded coachman on the box.