While I have a lot of problems with some of the Boston sports fans, I don't completely agree with this.
I actually think the majority of Boston sports fans are pretty good. The problem is, there is a very loud group who are insufferable, conceited, bandwagon jumpers. These aren't the core fans, and they aren't even the "pink hats". They are the guys who only care about the teams when they are winning, at which point they are their biggest fans. They also tend to be the guys who call into talk radio, and go to the games with the goal of making an impression, whether it is by starting the wave by themselves, or proving to everyone around them that they know the most about Boston sports. They are the guys who are at a random concert, and feel the need to start a "Yankees Suck" chant. They don't really care about the team, they just want some attention for being the biggest fan.
I think the majority of Boston Sports fans are relatively level-headed, knowledgeable, and loyal. Unfortunately, these are not the fans that often end up representing us.