Mets fans are bound by nature to hate the Yankees and the Braves. Maaaaaaybe if you recently became a Mets fan, you think you are bound by nature to hate the Phillies because they've been so recently dominant but you would be wrong.
It is difficult to hate the Cubs. They got a nice park and a lot of history and they're rarely successful enough to have any true emnity for 'em. If it is an extension of a pre-existing regional rivalry translated to baseball, as with the Cards or White Sox, I guess I get it but otherwise, it is difficult to hate any team so preternaturally doomed season in and season out.
I grew up and currently reside in extremely rural northern New York state and I'm a once-and-future Californian.
My attitude on hot dogs is less a regionalism and more just sort of an extension of my general "don't gild the lily" feeling on the topic of food.
If you got a really good food thing, why smother it in so many extraneous add-ons that you can't taste the food-stuff?
Mustard. Diced onions on special occasions. Anything more than that, I guess, why are you eating something you can't taste?