Merkuri
Explorer
I feel like in-game actions should have in-game consequences, and out-of-game actions should have out-of-game consequences.
As others have said, if the players are all okay with it then there's no need to take out-of-game steps. However the DM should (as always) make sure the game world reacts realistically to whatever is happening. If one PC kills another in front of a city guard, then they're likely to get arrested.
But if it's affecting the out-of-game feelings of the players - making things less fun for people at the table - then the DM should address it out-of-game, perhaps by taking the problem player aside and letting them know they're making things less fun for others. Some problem players simply haven't thought things through and don't realize they are being a prick, so when you bring their attention to it they'll stop. If they don't get the hint then it may be time to boot the player or, as HoboGod mentioned, just tell them, "No, you can't do that."
If a player is being a prick it will probably do no good to punish him in-character by making NPCs not talk to him, lightning striking, or the like. That sort of thing is either not obvious enough for the player to catch onto or so obvious that the player will feel like they're getting picked on and the behavior may get worse as the player acts out.
Especially if they don't realize they're doing anything wrong, punishing somebody without letting them know why never helps solve the problem.
I've done a lot of research into animal training, and if you're going to punish an animal you need to do it immediately after the problem behavior, or while the behavior is going on. The animal needs to associate the punishment with the behavior in order for it to learn to stop that behavior if it wants to avoid the punishment. If a dog pees on the floor while you're at work and you hit him with a newspaper when you get home it just teaches the dog to not like newspapers (or not to like YOU).
With humans, it's a lot simpler. You can just tell them what you don't like. Talking usually goes a lot further than trying to passively affect their behavior with in-game punishment.
As others have said, if the players are all okay with it then there's no need to take out-of-game steps. However the DM should (as always) make sure the game world reacts realistically to whatever is happening. If one PC kills another in front of a city guard, then they're likely to get arrested.
But if it's affecting the out-of-game feelings of the players - making things less fun for people at the table - then the DM should address it out-of-game, perhaps by taking the problem player aside and letting them know they're making things less fun for others. Some problem players simply haven't thought things through and don't realize they are being a prick, so when you bring their attention to it they'll stop. If they don't get the hint then it may be time to boot the player or, as HoboGod mentioned, just tell them, "No, you can't do that."
If a player is being a prick it will probably do no good to punish him in-character by making NPCs not talk to him, lightning striking, or the like. That sort of thing is either not obvious enough for the player to catch onto or so obvious that the player will feel like they're getting picked on and the behavior may get worse as the player acts out.
Especially if they don't realize they're doing anything wrong, punishing somebody without letting them know why never helps solve the problem.
I've done a lot of research into animal training, and if you're going to punish an animal you need to do it immediately after the problem behavior, or while the behavior is going on. The animal needs to associate the punishment with the behavior in order for it to learn to stop that behavior if it wants to avoid the punishment. If a dog pees on the floor while you're at work and you hit him with a newspaper when you get home it just teaches the dog to not like newspapers (or not to like YOU).
With humans, it's a lot simpler. You can just tell them what you don't like. Talking usually goes a lot further than trying to passively affect their behavior with in-game punishment.