I was playing Lord of the Rings Online one night when a player agreed with something mentioned in general chat by saying "Indeed!" Without rancor or hostility another player laughed at this stilted language and asked whether people really talked like that. Of course the question was answered with a chorus of "Indeed!" but in the ensuing conversation the player who had laughed said that he or she was from an economically disadvantaged area where the use of language like "Indeed" was wholly foreign. S/he was surprised to discover that language differed so radically among different socio-economic groups. And I thought, "Now, this is one of the reasons why MMOs are such interesting places."
People categorize each other based on visual attributes like age, gender, hair and clothing style, and skin color. We also use political, religious, and social ideologies, musical, cinema, and leisure time preferences, and socio-economic class differences to divide ourselves up into different groups. The tendency to categorize and divide has more to do with the basic functioning of the human information processing system than bias or narrow mindedness on people's parts, and it is useful in allowing us to function effectively in the complex, dynamic, and often dangerious environment we call the real world. However, it does have it's drawbacks. It's long been known that people have a marked tendency to identify themselves with a group, identify people who are not members of their group as members of an out-group, and assign negative characteristics to the out-group. Moreover, we tend to spend most of our time with people who are like us. In other words, we hang out with people who look and think like we do and tend to think about people who are not like us in negative terms.