It's common knowledge: people from San Francisco hate Los Angeles and everything about Los Angeles and everyone from Los Angeles.
But why? I'm from LA and I lived in San Francisco for ten years and I never fully understood it.
It seems like the one socially-acceptable and regionally unique form of bigotry in the country promoted by some of the most self-righteous, professed anti-bigots that exist.
It's not just a "sports-rivalry," either. It's much more virulent and personal. At least for the people in SF. In LA, not so much.
Jack Rudy, another person who's lived in SF and LA besides me, explains his take on this cultural phenomena.
You don't have to agree with it. But then, if you don't, you're wrong.