The question was ask how you became a fan of your favorite team, let's ask now, how did you come to hate your least favorite team?
trhe biggest rival of your favorite team(s)....as this applies to me
Giants fans hate the Cowboys...
Devils fans hate the Rangers.
Mets fans used to hate the Cardinals. But now that doesn't apply..Now we hate the Braves and their fair weather fans.
And as far as neigborhood rivalries. On my street you were a Yankees family or Mets family.