Luckily I've never had an unwanted player situation, however I have played in a game where I didn't care for anyone else in the game. They were all a bunch of rude loudmouths and racist to boot: Once they started to refer to monks as "gooks" or "chinks" I just quit.
If I were to ever encounter a situation in which I wanted to get rid of a player, first I'd have to make sure this person really is a disruption or whatever for others as well, and it's not just me getting irritated at him/her.
Assuming others find this person troublesome I think it would be best if one of two people ask him to leave: Either the DM (sorry, DMs, this is one of your "other duties as required), or, more ideally the person who initially invited this person to the game, if there is such a person.