I have a rule at my table, heroic (good) characters only. I don't mean lawful good paladins, but no one is allowed to go out and destroy the world, good NPC's and the like. Yes, that is quite restricting in many ways, but the players all know that going in and agreed to it, plus it makes my life a whole lot easier as a DM.
I have a homebrew, but one of my players (a very argumentative one) wanted to play his halfling rogue like a kender and I said that was okay. I understand kender have a tendency to "acquire" items, which I believed could create some problems with our heroes, but it could still be role played well and not be too detrimental. Again, I don't want them to be lawful good paladins, just not evil. Tasslehoff from the Dragonlance series came to mind, occasionally a nuisance with his acquisition of items, but didn’t outright hurt the group.
The problem I am having is his character is actively trying to steal everything, from NPC’s to the other players. He hands me a sheet of paper with his thievery checks, and if he rolls what he considers too low, a bluff check to bluff his way out of it. He runs off to find creatures or other great dangers that the group is not capable of handling (they are level 3). Hey, if he kills himself, that is his problem, except it interferes with the group, splits the party, puts them in danger as they are now missing their striker, and in general causes problems, especially in a story heavy campaign. I want to be clear that the rest of the group (the other five players) are completely on board with the story heavy aspects of the game and understand the importance of certain actions and their repercussions.
I already have the rule in place about playing heroic, but I try to let my players do what they want and not railroad them too much, and I fear that taking dice rolls away or not letting him wander off as his character would do would be too control on my part. I already plan to do away with his bluff checks next to his low thievery rolls as that is blatant meta-gaming, but what can I do to reel him in so he doesn't hurt the group while not killing his fun in RP just because it doesn't mesh with the rest of our play style? I never go out of my way to punish a player for having a different play style, but I do not want to let it become a further problem for the group, who are showing some frustration.
Sorry for the long windedness of my post.