1
general::
Phrase(s): swear like a trooper
to curse and swear with great facility. (The trooper here refers to a soldier.) • Mrs. Wilson was known to swear like a trooper on occasion. • The clerk started swearing like a trooper, and the customer started crying.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Freely utter profanity or obscenity, as in The teacher was shocked when she heard one of the fathers begin to swear like a trooper. The troopers in this term were the cavalry, who were singled out for their swearing from the early 1700s on.
American Heritage Idioms