In response to your second question: It's more fun to argue about sports, but it's more interesting to argue about music. When someone argues about music, you can usually get a remarkably clear portrait of their personality -- you can get an idea of how they view authority, or if they have an adversarial relationship with mainstream culture, or if they are extremely worried about being cool. You can deduce which subcultures they experienced in high school, and you can figure out how much they are engaged with modernity. Of course, the downside is that people who always want to talk about music tend to be profoundly annoying (and often unshaven). Which is probably why it's more fun to talk about sports.
Arguing about sports is the ultimate cultural equalizer: I can't think of any subject that so many people know so much about. I feel like I personally know at least 100 guys who have a "near expert" understanding of the NFL. If you watch the games each week (and especially if you grew up watching the games each week), you can easily have a 90-minute conversation about pro football with a total stranger in any airport bar (assuming said stranger has had a similar experience). There is a shared knowledge of sports in America that is unlike our shared knowledge of anything else. Whenever I have to hang out with someone I've never met before, I always find myself secretly thinking, "I hope this dude knows about sports. I hope this dude knows about sports. I hope this dude knows about sports." Because if he does, I know the rest of the conversation will be easy.