I've kicked out three players over my career, we'll call them A, B, and C.
Player A was the type who always played the same kind of character. It was always a thief/assassin, always wore black and always hid in the trees. This includes a post-modern setting, far future, fantasy, whatever we played, thats what his character was. We talked to him about it, but in the end, it wasnt enough to make a fuss over. At least we always knew we'd have a lock-picker if we needed one. What became a problem was his style. Lets put it this way, this is a more or less typical session:
Player A: "I pick his pocket."
DM: "Again?" sigh. "Roll it."
Player A: "13"
DM: "Ok, you find a silver coin, he doesn't notice it. Anyway, up on the dais..."
Player A: "I pick again."
DM: "What? You just did."
Player A: " I know he has to have more on him than one coin."
DM: "All right, but this is your second try, it'll be harder."
Player A: "I know. 2."
DM: "This time you dont get anything, and he notices a tugging at his hip, he sees you, and calls out. The guards on the dais..."
Player A: "That can't be right! Look at my pick pocket skill, thats too good for a peasant to notice even with a roll like that!"
As I said, this was typical. He'd even try to pick his companions pockets during combat. If I made him fail, it turned into an argument. If he succeeded, it only encouraged him. His justification was "This is what a thief does!"
I was dropping hints in game that were far from subtle and he just kept at it. Every game. I finally decided to scrap my campaign and start fresh. I wrote up what the allowed classes and such were going to be, explained what kind of game we were going to play, put in t a few minor restrictions to get him to abandon the thief type he always played. He finally caught the hint and left, but not before sending me a nasty email about how I was the problem since if a player didnt fit my style of game, I'd try to limit him and make it so he couldnt have fun. That may not have been the best way to handle things (and there were out of game discussions as well, both as a group and individually as well), but you live and learn.
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Player B is another kettle of fish. He is the type that promises to be there and then isnt. I make it very clear to all of my players what my attendance policy is. The problem is until he joined our group I had no need for such a policy. No warning. No polite emails or phone calls. He'd just not be there. Most times, I wouldnt find out why he wasnt there for several days after. About 75% of the time, it was a simple "There was a game that night? I forgot!"
Yeah sure. I spent part of my time between sessions sending out a newsletter. One of the things I made sure to include was the date and time of the next game (which was always at my house, 6 pm Wednesday, every other week. It never changed except for holidays.) The lamest excuse was the one where he left on a two hour road trip earlier that day for a 'love thing. You wouldn't understand.'
I talked to him out of game about it. I gave him more than his fair share of chances, but after two sessions or so, he'd go right back to it. This guy was a problem out of game as well. "You wanna go bowling?" "Sure" Then he wouldnt be there, wouldnt answer the phone. "Hey we're going to go catch that new flick, wanna come?" "Sure" No show. He was set to buy a dragon sculpture from me. Every time his day off of work came, he'd assure me he'd be there with money in hand. Then he'd forget.
I stopped inviting him to games, stopped taking his calls, and he still wouldnt catch on. Then one day he called, I answered and he wanted to do something again. I told him plain out and bluntly I wasnt interested, and here's why... Like usual, he apologized, swore he'd try harder. He's still doing it. I cant make it any more blunt and to the point than I already have, but it wont sink in.
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Player C. Okay this one has a happy ending. My wife knew player C when they were both in grade school...the stories she tells about how he acted back then...
Anyway, he got invited to join our grou pbecause of mutual interests and a desire to increase the pool of players we had for Star Fleet Battles. He insinuated himself into our RPG's, everything we did. Now, aside from a bit of thick-headedness, he was a pretty nice guy. But he liked to argue. With everyone. About everything. And not a lively debate, a shout at the top of your lungs you're wrong, and I'm right kind of affair.
Then I made a mistake. I allowed him to play an immortal. Well his in-game persona took on many of his out of game aspects and this immortal gunned down an entire store full of innocents. "I'm immortal, what can they do to me?" The discussion about how that wasn't cool degenerated into another argument. I mean he knew most of the rules, but got a fair number of them wrong. When the rules were interpreted against him, you guessed it, shouting match time.
Ok, so we decide to do something about it. We hold our out of game discussion, he agrees but says "thats just the way I am." WE warn him again, and for the first half of the next session, he seems to finally have cooled off and learned how to play nice. Then things go rotten again. So we decide to get rid of him, he's too much of a stress on our game. I arrange a way to kill his PC and give him a chance to save it. Outside of the game I told him, you get one more chance. He blew it, so the kill went in and we told him not to come back. He argued and screamed and eventually left.
Now for the happy ending. Less than a month later, we start letting him come over on a limited basis again. You'd be amazed at the turn-around in this guy. He still has a temper, still likes to argue, but he is more calm and reserved about it, and he will actually listen to what you say. In fact, he will actually accept it now if you can show him where he is wrong. He is a completely different person in game and out. My wife is surprised by how much of a difference there is. She likes him, where before she only tolerated him. He's my best friend now, and the core of my gaming group. Whatever we play, he wants in. He can hold a steady job now (something his temper prevented him from doing before).
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In each of these cases, there are a lot of details that I have neglected to mention. The above are watered down versions. (Think how long this post would be if I went into detail!). In every case we tried to resolve things peacefully outside of game time. In every case, I was not the only player who was bothered by their actions.
However, I have learned a lot from these three experiences. I make sure I know the people I game with. I play short duration games to see how they get along with others. Heck if I'm going to consider playing with a stranger, I meet him outside the house just to get to know them first.
That really is the key..make sure you know who you are gaming with. If you cant be friends with them outside of the game, then inside the game, it just isn't going to work out.