There's actually a slight mechanical reason I would think about going chaotic evil in 4th edition, and that would be to use the channel divinity of an evil divine path/domain. If that's the case, it could easily be overcome by you saying to the player "choose something else and you'll get the same benefit as the evil one" - because your the dm and you can rewrite any rule. Also, sometimes a dm wants to run an evil campaign. With regards to rewriting any rule, you could offer up a "chaotic evil / evil divinity" that has the precept of having to - essentially - cooperate with the group of pcs - because in your campaign you write the world as the dm. Perhaps an item that is living and evil as well, and exerts a will to travel with the group and cooperate with them. Perhaps the evil character is on the run from another evil character - a villain haha - and needs the heroes to survive throughout the entire campaign, hahaha. Might want to look at it differently. However, me and the others on this page and probably in the campaign might not like it if that player is going to be evil to the group , so put those cards on the table with the player so they don't do that. Headhunter Jones said: On that note, you might consider my standing rule governing PVP:
If you attack, steal from, or otherwise attempt to hinder another
player's character, the target character's player decides the outcome.
No dice or game mechanics (which don't support this sort of conflict
anyway) will be used. Be aware of that pvp nonsense. I wonder if it's an example of "Yes, and" where the dm and the player could together create a story about that evil character which makes it more fun? If you don't feel comfortable doing something like that yet, then maybe you should just do something else.