Not sure, Narile, when Twain said this but if he didn’t do it before 1859 he was not the first. This is a bit of a hobby of mine so I checked the OED. Yob is backslang for the word boy and meant simply “a boy, a youth” throughout the nineteenth century. In 1918 it was used by soldiers to describe “an officer or one who is easily fooled,” but that particular meaning seems to have disappeared and the word acquired the pejorative sense given above (“a lout, a hooligan”). An example that seems to justify TomH’s dislike of the term is given from London Times in 1984: “I would not want anybody looking at me to think this man is a thick, stupid, illiterate yob.” Even more telling is (the ever-irritating) Sunday Telegraph also from 1984: “The loony Left should not be confused with that other Left which has been described as the Left of the yobbish tendency.”