Cfrgtkky

It sounds like you've done a great job handling this thus far. You have talked to the players individually and in a group setting, collaboratively created a set of play guidelines, and made sure that expectations are clear. Good job! While these strategies tend to catch about 90% of interpersonal issues, it's clear that they aren't working in this case. I have a theory about why that may be. It's something that comes up fairly frequently with new players.

RPG Confusion, aka "Is This a Video Game?"

My suspicion is that your player is unaware of the differences between a collaborative storytelling game like 5e and an RPG video game (Assasin's Creed, Grand Theft Auto, etc.). In a video game, the creators have made the world and handed it to the players. They typically no longer have any direct control once the players enter the scene. They have pre-defined the type of interactions that are permitted and placed bounds as they wish. If the game makers allow you to kill NPCs through a variety of gory means, then that is clearly meant to be part of the game and no one will get upset with a player for playing that way. If the game allows you to sexually assault characters, steal from them, etc., then those things are a valid form of play, and everyone can expect that players are consenting to be exposed to that sort of content.

Story-telling games are great because they don't have the restrictions that video games have. You can, quite literally, "do anything you want." However, that freedom requires boundaries that the players have to set to make sure that everyone is having a good time. You're obviously familiar with this concept, but I think the issue with your player is that he doesn't comprehend the difference. He is used to being able to do whatever he wants as long as the game physically allows it.

How to Talk About The Issue

My recommendation is to have another 1-1 talk with him and cover some of the following points openly and honestly:

1. 
   He is preventing the other players from having a good time - This game is collaborative. The number zero rule is that a player cannot do anything that takes enjoyment away from anyone else at the table. His actions are violating this rule. Give a specific example of something he did or said that made someone else uncomfortable. (get their permission to use the example first)


2. 
   He is in charge of his character's actions and personality - Saying "but that's what my character would do!" is a cop-out. He is choosing to make his character an asshole. If he wants to play an asshole, that's fine (maybe). But he needs to do so in a way that doesn't violate rule number 0.


3. 
   You are happy to help him brainstorm in character actions - If he is having difficulty thinking of things to do that wouldn't break rule 0, he should ask for help! There are so many ways to be an asshole. Surely you or someone else at the table would have some ideas for more interesting things that a chaotic evil character can do.


4. 
   He is welcome to roll a new character - If he feels like it is just in his character's nature to rape and murder, then maybe that character should be caught and face justice and he should play as someone else who doesn't want those things.


5. 
   You want him to have a good time - What is he hoping to get out of playing this game? Probably fun time with friends? Maybe make new friends? Emphasize how playing within the group's rules will help him meet those goals. If his main goal in being there is having a power fantasy, then this just isn't the game for him.


6. 
   Video games vs co-op story-telling games - For another example of this, see the "Minecraft example" below.


7. 
   You want him there, but if it isn't going to work out, you may have to ask him to leave - be upfront with this possibility. Tell him that you are confident that he can be a positive influence on the group and that you're sure he has a lot to offer. Mention an example of something good that he did. An actually funny thing he said, a piece of creativity, etc. as evidence that you know he can contribute in a positive way. However, be clear that if his presence is making other people have less fun, he won't be able to keep playing. That would be a huge bummer for everyone since they'd lose out on him being there.


8. 
   Ask him to think about it and get back to you with any questions - Let him know that you are happy to talk more about it if he wants, but that the ball is in his court, and it's time for him to commit to having fun. Tell him you'll see him at the next session, and mention that you're excited to see how the party will (handle lots of enemies, get the secret from the minister, face the dragon, etc.). Leaving on an anticipatory note will encourage him to look forward to the future.

The Minecraft Example

I teach at a technology summer camp, and I often play a simplified version of 5E with my overnight campers (age 10-17). With the younger kids especially, they can have trouble keeping in mind appropriate behavior and understanding co-op games, just like your player. I talk about Minecraft to get them to start thinking about how to help other players have fun. You're welcome to use this directly (with maybe more adult language), port it into some other game, or ignore it.

Nearly everyone has played at least a little bit of Minecraft. It's a really great game. It's most fun when you can play with other people and build together or compete against each other. But playing together can require a lot of trust too. It opens up your world, a place that you've spent hours building and making just so, to people who could come in and destroy it.

We're doing just that. When we play a game like Dungeons and Dragons we are all creating a world together. Everyone contributes and has opinions about what the world is and what it should be. In Minecraft, when we play together, we establish ground rules to prevent anyone from destroying the things that someone else has built (like no TNT) or to set when destruction will be allowed (maybe you can kill someone if they agree to it). When we play this game, we do the same thing. When you hurt someone else's character without permission from them, when you act in ways that the group has agreed are not allowed, or when you ignore what other players want, you are no longer working as a team. Instead, you are destroying parts of the world that those players have built. And that makes the game less fun for everyone, even you.

His Response and Some Further Thoughts

I'm not sure how he will respond to your open discussion of the issue. While we hope that all adults know how to cooperate and how to take constructive feedback, it's not always universally true. There's a possibility that he might rage quit. There's a possibility that he might think about your words and make real change. Who knows. But if he gets angry when you tell him the truth, then you really didn't want him in the group.

In the best case scenario, he thinks about what you say, realizes that you're right, and changes his behavior. You will likely still have to remind him periodically or cut him off if he crosses a line, but that's okay. If he's trying, then you can work with him.

In future situations of this sort, it may be useful to consider not letting new players play characters who are chaotic or evil. I find that it just never seems to go well for their first game. I'm sure that some GMs don't have an issue with it, but I personally do so I just have that policy. As a note, I also never let a player play as a character that is inherently cruel. That's just not a character trait that I'm interested in exploring.

As you guide players through character creation, feel free to limit their ideas in these or other ways. In my experience, doing so will actually help push them to be even more creative and craft more interesting characters that are not simply stereotypes.

Good luck! I hope that everything works out!

No getting around it, and no need to work with in-game punishments. In-game punishments make the problem just another part of the game, and this is more serious than that.

You've got to be blunt here: you have an agreed code you expect players to follow. If the player starts hurting your game like this, you can and should inform them that they're no longer welcome to your game if the behavior doesn't change. In other words, an ultimatum. It's one of the more difficult parts of friendship giving this kind of feedback to someone you might like otherwise, but they just have no right to make others uncomfortable like this.

If they get defensive and point out that it's their character's personality, calmly remind them that they were aware and agreed to the rules in which case a Chaotic Evil character was probably a very bad idea (as it often is). You can always offer them to have a fresh start with a new character, or retcon their current one, if the player thinks their current character is a hindrance to playing by the agreed rules.

While @kviiri's answer is probably your best bet here, it's the nuclear option. There is a step you can take before going there, based on your description of the problem. You said:

one of them started [...] describing explicit sexual actions

You're the DM. You can, and have the authority to, put a stop to this by wielding your DM powers to fade to black and cut to a different scene. If the player starts narrating something that makes you or the other players uncomfortable, interrupt him with:

Okay, you're doing that. Meanwhile, over at the tavern...

And immediately move on with whatever's going on in the other area. Don't pause - make sure you have your narration ready, don't give the player a chance to interrupt. You will have to be very firm with the player as they're likely to do everything they can to get the scene back. Handle this by repeating, as many times as necessary:

That's happening off-screen. We're going to focus on what's happening in the tavern now.

The key here is the repetition. Remain polite but absolutely firm. Never give the player more description of his desired scene than "that's happening off-screen", and don't allow him to describe it himself.

This takes away any gratification the player gets from describing these graphic scenes, without you getting drawn into futile arguments about Session 0, or the player making empty promises to stop. Instead, you're training the player that there is nothing to be gained by trying to push this on the group. They don't get the pleasure of imagining these scenes out loud, they don't get pleasure from watching everyone else squirm, they don't get to be in the spotlight.

This tactic effectively counters the "my guy" argument by allowing the player to be the "my guy" guy, without allowing him to disrupt the rest of the group's fun. His guy is CE and likes to do twisted, depraved, graphic things? Fine, but it's always off-screen and never (allowed to be) described in detail. It's never given attention, it's never able to get detailed enough to upset everyone else.

If the player is a reasonable person, eventually they'll get the hint and stop trying. If not, they'll likely remove themselves from your game, which also solves the problem.

This tactic generally works best on people whose "my guy" syndrome (MGS) comes from a place of innocence, such as being too new/young to understand table etiquette. MGS players who are deliberately using MGS as an excuse to get away with bad behavior are less likely to respond to this tactic, and may even escalate their behavior in retaliation. If a player does escalate, then it's time to boot them. Your job as the DM is to make the game fun for everyone, and that includes the sometimes difficult task of kicking out a disruptive player.

Welcome, Yoko Msps.

First, it is a personal declaration of principles for me that no one should be made to feel uncomfortable at my gaming table. This means, among other things, we're going to keep the tone of the game at a mutually acceptable level. I say this to make this point: I agree with your instincts here that something is wrong (due to your and the other players' discomfort) and that it needs to be fixed.

Second, I think you've gone at least an extra mile with this player: You've laid out your guidelines, you've backed up and re-run your guideline process to include him, you've gotten an agreement from him, and he's violated it again. These do not sound like minor infractions.

Third, his justifications are a pure "My Guy" defense, of a variant which just covers for anti-social behavior. If your instincts are to disregard that defense, those instincts are also good instincts.

But in my experience, punishing players almost never works. It mostly leads to an adversarial stance between the GM and player. Indeed, the bigger the infraction, the bigger the punishment tends/needs to be, but this just tends to deepen the adversarial positions. I can't easily recall a situation where a GM successfully broke another player's will, and I can't imagine it would be that satisfying anyway.

You could, I suppose, let the game world punish the character (rather than you directly punish the player) if the character is taking in-game actions that are criminal, anti-social, or otherwise questionable. But I have to be honest, this usually works on the first shot or it all goes sideways in my experience. Given that you've warned the guy already, I don't see this as having a high chance of success.

The only thing I can think of, if you really want to give this guy a second (or third) chance, is to let him ("let") make a new character that isn't so disturbing. At some point, though, you do have to prepare yourself to follow through on the last resort of booting the guy from your table.

Finally, to answer your question, no, I do not believe the fault is yours by lack of stern-ness. You shouldn't have to come across like a tank just to make a basic point about civility and table standards.