As a Bruins fan, I'd argue there's a good chance they are. Definitely in the top 5 disliked. I'd put Montreal in there being they are the NY Yankees of hockey. Maybe Chicago because this decades success. Toronto because of the fanbase penciling in future cups/thinking it's a birthright. Detroit? for the history.....Carolina moving up because of the surge.
1) Boston sports as a whole is hated....although the Bruins winning....not so much. For the record, I don't like any other team in Boston and would happily trade all their championships for 3 or 4 more Cups.
2) Marchand. Look, Even I think he's too much sometimes.
3) Historically, Boston has always played a certain way that does not make it easy to face them. That said, I don't think every recent version of the Bruins has been as gritty as say, this year's club or the 2011 team. Same thing goes for the Flyers historically.
Edit: Forgot Pittsburgh. Yeah, they are still the most hated I'd say.