See also the Boston Brahmin accent, 'an affected set of speech patterns whose "chief quality was that no Americans actually spoke it unless educated to do so."'

There's some evidence that the accessibility of a given accent is at least partly dependent on genetics... I've got a fairly strong Celtic heritage. A once-companion warned me about Geordie, the accent around Newcastle-upon-Tyne... but I had very little trouble with it. OTOH, when Sir Patrick Stewart (a past master of RP) yards out his native Huddersfield (Yorkshire) accent, eeee, lassie, I dinnae ken a word out 'is gob! (FWIW, that's Geordie I was using.) Sir Patrick recites an old Huddersfield poem...