I had to kick one single player from our group.
One problem was that at the time, it was getting really crowded at the table, and a couple of players were telling me that they thought the table was too small for so many people. I probably wouldn't have kicked him just because of that, but there was more:
His characters didn't fit in. I was running two games at the time - a short Vampire game, and my D&D FR campaign. The Vampire campaign (which was Requiem, not the old Masquerade) was supposed to run like it says in the books: the kindred running a low profile, crimes potentially resulting in loss of humanity (and ultimately turning the character's control over to the ST. The other players had no problem with this, and their characters fit in. Not so his character. He was some criminal kingpin type or something, and he got upset (more about his brand of upset below) when he couldn't run through the streets laying low people with machine guns and awesome vampire powers.
The FR campaign had its focus on good characters. Didn't have to be stereotypical, but they did all have an advanced version of the aasimar template (basically the Selûne-worshipping light counterpart to the shades, though not as strong as those. They were affiliated with the Conclave of Opus and at war with the shades). His character was a half-orc who apparently didn't bother too much with moral issues.
The "fun" part was that he complained (before he even started in the game - another player introduced him and spoke highly of him) that the game was so combat focussed, and then he proceeded to build a fighter/barbarian that was well within the realm of powergaming.
About his brand of upset: When he didn't like something, he demanded to know why it was so. No, he didn't ask. He demanded. In a tone you would expect from someone demanding what you are doing with his wife, naked, in the bedroom.
This was made worse by his... "lack of knowledge" about the rules, or certain parts of the rules. It usually went like this: He'd find some nice loophole, put it into his character, I found out and told him that that wouldn't work, and he'd shout "WHY NOT?". Sometimes, it was stuff that was weakened in 3.5e and he still used the 3e incarnation (often stuff that was weakened for good reason), or he "missed" parts of the rules that made his little tricks impossible.
Two examples were using two gloves of storing (because they were way better than quick draw), for 2000 gil each, and when I told him that they cost 10.000 each (changed in 3.5), he started to argue that he's absolutely sure about it (showing him the passage in the DMG shut him up of course); and trying to use rune magic to ensprell arrow heads with explosive magic to shoot half a dozen fireballs per round (the rune magic rules explicitly disallow that, as it would be way too powerful).
He managed to wear down my patience in two game sessions, and while I was thinking about disinviting him, the others were commenting about the space problem, we got to talk about the guy, and spontaneously decided that he'd not be welcome any more.
Shortly after that, his friend left the group, too, but that wasn't too much of a loss, either. Though this was his first D&D game, he'd often come up with ideas like permanent true strike on a weapon for a pittance, and tried to argue about it when I forbade it. In retrospect, I guess I know where he got his ideas from.
About how I kicked him out: I didn't have his number, so I called his buddy, and asked him to tell his friend that we couldn't invite him into the game again.