The act of letting loose a long string of expletives and curse words. Usually brought on by pain, frustration, or drunkenness. The term "Swear Train" has its roots in 1885 in Topeka, Kansas, when famed Weston Hughes fell off the roof of an express train and swore for a record three hours.
Joe: Did you hear the Swear Train that Bobby let loose when Teresa kicked him in the balls?
Dick: Dude, that must have been one hell of a long train!