Taste Tribes
There's a great line in the film High Fidelity where the main character, Rob (played by John Cusack) makes the observation that he doesn't like people because of who they are – he likes them because of what they like.

At first glance, this position sounds incredibly superficial. But on closer examination, it becomes more reasonable. After all, why do you talk to the stranger in the coffeehouse or in the bar? Unless you're a creepy freak who just bothers random strangers, it's probably because they're wearing a t-shirt sporting the logo of a band you like or reading a book by your favorite author. This spurious connection gives you a reason to talk to them.