The most important thing is to make sure all conflict stays confined to the game, and doesn't spill out into the real world. That is to say, if Joe is being a jerk with his in game actions, Mike needs to respond to that as if Joe's characters were doing the actions with actions that are appropriate for Mike's character. There are so many conflicts that can be deescalated at this level by most or all of the player's involved not taking it personally and not getting their ego involved and avoiding the temptation to anger. And I agree with delricho: the worst thing you can do here is let a player act like a jerk through his character and not face consequences. If a character is continually screwing his own party, the appropriate thing might be to just let the party kill him.
The second most important thing is for the players to as much as possible play for consensual outcomes to the conflict that allow the game to continue. If you the DM see that what's about to happen is about to spill over into personal vendetta, it's time for you to take off your referee hat and put on your director hat. It's not your job as the DM to fairly arbitrate a lethal conflict between party members unless it's first agreed out of game that everyone is happy with the idea of this going lethal and is thinking rationally about how it will benefit the game, and not simply using their playing pieces to take out their frustration with another player. You need to stop play, and get people to talk about what they want from this scene before going forward. If someone has just basically said, "Eff the opinions of another character/player", you need to stop play right then and ask whether they are content with any outcome that might result from that, find out what outcome they might be willing to accept without getting angry, and try to find some way to settle the group down and accept results that aren't pure ego on the part of the players.
In general, what I find is the basic problem is you have a group of players that are used to resolving every problem they have in play with violence, and suddenly they find themselves facing a problem where violence is not a productive solution for anybody. And basically you have one angry person dare someone else to result to violence, and yeah - that never ever works out. Usually its a very good rule to assert that the party will agree to resolve the situation with violence, but that ultimately no one is going to kill anyone else. Ultimately, the group is going to remember that they are friends and find an excuse to not kill. Ultimately it may mean some character has to offer an apology, and the character's need to work out there differences in some fashion - even if its something like, "This isn't over. I can't afford this right now, but as soon as we kill Xykon; it's on."
Once tempers have calmed down, once the party has agreed to a plan, then you can move forward. In your role of game director, when you call 'timeout'/'cut', you aren't ship's counselor Troi. You are the boss. You don't need to defer to anyone. Yes, people need to discuss feelings, but its more important to discuss the scene - what it means to them, what they want, where they see it going. Your role is to help arbitrate that and advocate for a solution that to you seems fairest to everyone involved, and gets the game going again.
That might sound something like this:
Paladin Player: Look, if activating this door is an evil act, then we have to find some way to work around it if possible. I can't just stand aside and let evil happen.
Warlock Player: I get that, but I'm tired of dealing with this freaking cliché door. Clearly this is a statutory chokepoint, and we aren't going to get past it unless we use the red key on the red door. But, if you've got some bright idea for getting around the door without standing around diddling it any further, be my guest.
DM: Both of you have good points, but this conversation between the Paladin and the Warlock would be a lot better in character precisely because you both have valid points. Obvious the door is frustrating the you, and so its perfectly reasonable that the characters are frustrated. Go ahead and express that. Just don't take it out on each other. It is after all my door.
Warlock: Which just means you want us to have a bunch of more time wasting with the door even though we know how to open it, and ultimately someone is going to stick their arm in the door.
DM: Good point, but in character please? You complain about time wasting, but this argument is wasting more time than the role-play would have. So unless you consider arguing more fun than playing, it's get back to the game. And Paladin, yes, activating the door is evil, but the code you are following allows for the possibility that you'll find yourself in situations where all choices are evil. If you can't find a way to open the door, you'll have to choose what you value the most and live with the consequences of that decision.
Warlock: Fine, I'll play the dang scene, but enough of the railroads.
The more mature the players are, the less this is a problem. That's because you have less ego driven players who are taking actions with full knowledge of the consequences and cueing off other people's actions. The warlock pushes the paladin out of the way, the paladin chops is arm off, and both players think that is just awesome because they are no longer thinking primarily about "How can I get my way", but "How can we jointly tell a story that people will be telling with fondness for years to come." As a DM, I'd even take off my normal hat of neutral refereeing impartiality +5 to make that scene more awesome - like changing the door from taking 1d4 CON to being a death trap that traps the arm and sucks the victim dry so that by chopping off the arm, the Paladin has actually saved the warlock's life.
The problem of course is that most highly experienced players are lousy players who don't think, "How can I play my character in a way that is most entertaining for everyone", but only think about getting their own way, flattering their ego, outdoing and competing with other players, and generally have an entirely dysfunctional attitude.