I hear those Yankee fans do rude things like throw beer on the opposing team fans, call them names, curse them, etc. (and that's when they're being nice--LOLOLOLOL!)
LOLOL, RooRoo! I was the COOK, so they HAD to be nice to me! Hahahahaha!
That's Mets fans you're thinking of. Yankee fans aren't --as a rule-- too rude to fans of opposing teams. I've been at Yankee home games against the hated Red Sox, and seen Red Sox fans treated decently.
On the other hand, I once knew a guy who rooted for Boston at a Rangers game in Madison Square Garden, and barely left with his life.