But seriously...
I, like BOSOX11, am no where near Boston (though not nearly as far away as LA) Living in central PA, I grew up a Phillies fan. Mike Schmidt and Lefty were my heroes. My father too, was a Phillies fan.
One day, he gave me a Boston baseball cap. "I know it's not a Phillies cap," he said, "But you have tons of those. Boston is good to root for, too." When I asked why, he said, "Because Boston is full of good Irish lads (he was very proud of his Irish heritage) and because it pisses off those sons-a-bitchin' Yankee fans!"
So, I wore the cap, a bit more and more through my teens, and I began to familiarize myself with the Red Sox here and there. College came and baseball was lost for me, for awhile that is. I began to get reacquainted with it in the late 90's and, for reasons unknown to me, I began to follow Boston and not Philly. Now, being a Boston fan in Central Pennsylvania in the late 90's meant that I'd see occasional stuff on ESPN and then later the playoffs. I really began to pay a lot of attention when Pedro was dealing and then then Manny arrived. By the time we got to 2004, I was hooked.
As for the "why"? Well, as my late father said, it really pisses off the Yankee fans around me. But there's just something about the those blinding white unis with the candy apple red "Red Sox" on the front. They've always seemed to have personality, too. Not always as much as those '04 guys, but never, ever the automatons that the Yankees field - the same haircuts, not smiling.
They have a "working class" feel for me. I know it's an illusion - they're all overpaid - but Boston is history and grit and lager. The Red Sox are Teddy Ballgame, Yaz, Fisk, the Royal Rooters, Tessie, and the Green Monstah! NY is crime, crowds, apple-tinis, and ridiculous red, white, and blue top hats. The Yankees are prima donnas, tantrums, bought-and-paid dominance, and STEINBRENNER.
When someone asks me why I root for the Red Sox and I need a short answer I simply say, "They picked me, I didn't pick them."