I've followed Dylan's career closely since '63 and the first time that I saw the term used was in 'Q' magazine, probably in the 80s. There were a lot of Dylan fans on the mag at the time (in every interview of other musicians, always asked was 'what do you think of Bob Dylan'). So they were Dylan fans - but they had to be 'cool' and just a tad 'irreverent', so they came up with a great monicker, His Bobness.