It seems like the Sox fans, mainly the bandwagon Sox fans, tend to be the most obnoxious. I've seen Orioles games on television where at least half of the ballpark was taken over by Red Sox fans.
I believe the same thing happens when the Yankees visit the Orioles. The reason why we Red Sox fans go down is part due to Southwest Airlines' ultra cheap fares to BWI, Baltimore's proximity to Washington DC and the experience of actually sitting in a beautiful modern ballpark instead of the broken down old ruin we have up here.
I agree that post-2004 bandwagon Red Sox fans can be annoying (although I think we were just as insufferable as miserable, fatalistic bastards). A good way to recognize the old Sox fans is that they're the ones usually hunched over watching the game intently, muttering stats and strategies and keeping their hands occupied either cracking peanuts or keeping score. New Sox fans are decked from head to toe in brand new gear, double fisting $10 lite beers, mispronouncing opposing players' names and obnoxiously shouting or singing 'Sweet Caroline'. Trust me, I hate them as much as you do.
Although, if Baltimore fans really hate Red Sox fans coming to Camden Yards, they should at least try and buy some tickets and shut us out.
I hate to bring it back to New York, but have you ever sat in the Bleachers at the old Yankee Stadium? Obnoxious is too weak a word to describe the fans there. I'm happy to see the new Stadium has drained all the life (and money) out of the them.