There should be an article written about bad Boston accents in movies. As someone who has one, some of the ones I’ve heard make my ears bleed....
Martin Sheen in the departed
That's a great point. Boston accents on film are uniformly awful, and on TV they are almost non-existent. I myself have a *moderate* New England accent, as opposed to a hard-core (that's: haaaahd-coahh) Southie barroom accent.
Even on Cheers they never quite got it right. The closest was Nicholas Colasanto ('Coach' Ernie Pantusso), who was born in Providence, RI. John Ratzenberger (Cliff Clavin) tried his best, but he's from the Connecticut suburbs of New York, which pretty much makes him a New Yorker. And Rhea Perlman is from Brooklyn, and it sounded like it.