Do you think that your son’s out there killing people?
Mac grew up as the son of a prisoner, who was very possibly arrested on a murder charge (Mac seems uncertain about whether or not his father has eaten someone, not whether or not he’s murdered anyone). There’s a good chance that he grew up with the people around him knowing this.
Mac looks like his father, he slicks his hair back to look even more like him. This could well have been a form of protecting himself, of self-preservation, growing up- after all he’s the murder’s son, what better way of protecting himself than giving people the impression that he might just take after him?
Except that his mother has also bought into the facade, thinks that he’s his father’s son. And she hates his father.
And with Mac it really is just a facade. Mac’s all bravado. (He’s the inverse of Dennis who’s managed to cultivate a normal exterior to hide the fact that he’s not safe. Mac has cut off the sleaves of all his shirts to show off his tattoos and muscles, Dennis has a uniform of shirts and jeans.) Mac’s learnt to survive by seeming to be tougher than he is.
And self-presevation is necessary for him. His mother has withdrawn from him. She seems actively irritated by his prescence. He most likely so much represents to her the man that has let her down so completely she misses the fact that Mac’s nothing like him.