I was trying to write a reply to https://rpg.stackexchange.com/questions/99829/player-abusing-narrative-freedom, but what do I know?
_I_ am the player with the power fantasies, and as a DM what I have done lately was just "the rules of the game do not support this. Also, stop trying to create evil characters. What about this good deity instead, and a story of being trying to reject your dark past? Oh, you've created an evil character who follows the good deity. OK, it's not like this will matter in my game anyway..."