We once played games where someone who loved the sense of control being evil gave him over the other players. He would often start a game as good, then gradually become a traitor to the group or do something that made him become the point at which the campaign revolves around. In both cases where this went to the limits, the games master/Dungeon Master failed to curb his impulses and it caused a severe rupture with the game. It became so terribly unfunny that multiple players quit. That is the result of letting an evil payer overrule the Dungeon Masters plans. If a Dungeon Master does not strongly reprimand this behaviour it ruins the play for the rest.
For me the best way to keep an evil character quiet is to not allow evil characters to enter or participate. Start off right and you can save everyone a lot of pain in the process.
If you tell a player that he can't have any kind of evil character then you may limit participation in your game. I can understand not wanting the whole party being evil but players should generally be able to play what they want within the limits of your world *wink*.
I feel that evil characters are fine but.... They must have respect for the other characters. No robbing the other PC's or murdering them in their sleep. This is a cooperative game. It''s not hard to make an evil character that has reason to function within a party for a campaign.
When dealing with NPC's etc I agree with what was said earlier. Actions have consequences. I can handle an intelligent evil character. I can't abide those chaotic stupid or evil characters who live to commit random acts of violence for no purpose other than disrupting the game and the fun for the other players. I'm sure that most of us have played in a game like that before.
Edited: Kyrroeth on 30th Jan, 2018 - 6:13pm
I feel like each gaming group has it's own social contract, and what is acceptable for one group will not be for another. I think that this problem highlights the need for a "Session 0" so that the gamemaster and players all agree on what type of game that will be played.
I feel people will play with people that think just like them if its in person. So if a group wants to be evil then that won't come off as a surprise or distasteful but very normal and exciting. This topic matters for a group that thinks playing anything but evil is normal and if you do play evil it shouldn't be total evil / chaos. So if someone wants to join in with a character like that I think the Dungeon Master needs to be the one that says it isn't acceptable.