Originally Posted by Kaplan
Well, that's one theory...
Interesting that Wikipedia doesn't support the HMS Blazer story. Here is their remark:
The term blazer originated with the red 'blazers' of the Lady Margaret Boat Club, the rowing club of St. John's College, Cambridge. The Lady Margaret jackets were termed blazers due to their bright red 'blazing' colour, and the term was adopted for wider use later. These early blazers were like later sports jackets, but this term has never referred to blazers, instead describing jackets derived from the later innovation of wearing odd jackets for land-based sports. Assertions that the name is derived from HMS Blazer are not borne out by contemporary sources,
although it is reported that before the standardisation of uniform in the Royal Navy, the crew of HMS Blazer wore "striped blue and white jackets", apparently in response to the sailors of HMS Harlequin being turned out in harlequin suits.