Let me outline why I find Red Sox fans to be obnoxious.
1. They think that they are the only ones who hate the Yankees. Fans of other teams have hated the Yankees forever. The only difference is that these teams actually got past them more than once between 1918 and 2004.
2. The fact that Red Sox fans go to other teams stadiums and think they are the only ones who know anything about baseball. The teams playing may have nothing to do with the Red Sox, but they will be there in scattered numbers and act like they run the place. They will find each other and yell at the top of their lungs "Go Red Sox" and until 2004, they would yell "Nomarrrrrrr!"
3. Their belief that no city has better fans than them and that no team has a better ballpark.
4. The obnoxious intellectuals who obsess over the Red Sox in the most nail on the chalkboard ways.
5. Their perpetuation of this idea that no other team in MLB matters and that it's just them and the Yankees and everything else is scenery and how they get the media to go along with it.
6. How they complain about how much the Yankees spend, yet they have often have the second highest payroll in baseball.
7. Whoops, almost forgot, I also get annoyed by them because they usually double as Patriots fans.