he's having treatment - he caught a dose of the coachmans
coachmans as in 'coachman's box' - old cockney rhyming slang for 'pox' (as with all cockney rhyming slang, only the non-rhyming part is actually used in speech)
"he's having treatment - he caught a dose of the coachmans" What is the definition of "coachmans"?