I agree with what a few other people have said about avoiding the problem until the group breaks up. Very rarely do problems get better when ignored, they usually get worse. After all, if you see a player do something that bothers the rest of the group and you let him get away with it time and time again then it'll probably just grate on the group's nerves until things come violently to a head. If the DM (or another player) were to talk with the problem player right away you have a better chance of either fixing the behavior or parting on good terms.
I think the big problem is that there are many different styles of play in D&D, and while it's possible to group people together who like different things sometimes you'll get one person whose tastes so completely clash with the group as a whole that it makes things difficult. What makes it even more difficult is when the players are friends to begin with. Nobody wants to tell a good friend, "Look, you just don't like playing the game the same way we do, so we want to cut you out of this group activity you love and have been participating in for a while."
Another problem may be that many DMs lack the appropriate leadership skills to deal with problem group members. In this case, a game group is very similar to an office environment where you have one person in a position of leadership (the boss) and a group of people "under" them who have to work together to accomplish goals. The difference is that a DM is not usually chosen for his or her leadership ability, but rather their creativity, ability to ad-lib, organization skills, etc. Being a leader is not generally a requirement for being a good DM, even though the DM is often looked to for leadership of a gaming group. If you don't have good leadership skills then it's often easier to ignore a problem (player who clashes with the group) than to do something about it.
I think what can help sometimes would be to make up a policy beforehand about how people can be removed from the group, as in my earlier post about Hussar's policy. Having rules to point to when repremanding a player can make it easier. Coming up with such a set of rules may be tough with such a freeform game as D&D, but it's possible, and may help if you run into players whose playstyle just doens't mesh with the group or who are just plain troublemakers.