In my office building, a couple floors down, is a person whose office window is filled with anti-Chargers posters. Now, not caring about the team is one thing (I certainly don't), and liking another team is still perfectly acceptable, but hateful posters? That's just being a jerk.
The kids in my class last quarter were asking me about football one day, and it was really funny how they assumed that everyone watches football and follows one of two teams.
Kid: Hey Miss, you a Chargers fan?
Other Kid: Oh, you're a Raiders fan.
Me: I don't really follow football.
Kids: Raiders fan!