I would play him as a character who doesn't want to do ANYTHING, ever. In the ability score damage section of ability scores, it states "A character with a Charisma score of 0 is not able to exert himself in any way and is unconscious." Compare to the others: wisdom - incapable of rational thought and is unconscious, strength - too weak to move in any way and is unconscious, constitution is flat out dead. I would say that the only reason you're getting up and going to eat and literally not starving to death is because that sandwich isn't really that far away. And it's already made. And it's your favorite. I guess.