I think people don't notice how emotionally closed off Mac is because he is the most friendly and open to being caring, but he keeps his internal world on lockdown. He does caretaking and people pleasing out of genuine care, but also to secure love without having to be vulnerable. He lets Dennis and Charlie reveal themselves to him while he doesn't reveal himself to them. Charlie can see through Mac, but Dennis and Mac can barely see each other on a good day. Dennis struggles with Mac's emotional withdrawal all the time. Sometimes Dennis lashes out because Mac isn’t emotionally present/hiding behind submission. (not to say it's justified for Dennis to lash out cruelly, just explaining.) He wants Mac to not hide behind people-pleasing and he definitely doesn’t want Mac to falsely suck up to him. When he scratched Mac it was because he wasn’t looking Dennis in the eyes. Dennis WANTS Mac to look him in the eye. That 's why dennis screams ‘look at me when you’re talking to me!’ when Mac still didn’t look him in the eye even after Dennis scratched him. That behavior from Mac read to me as his continued emotional avoidance to punish Dennis for his bad behavior. Dennis hates it. He doesn’t want a servant or submission, he wants Mac to be his friend. I’m not saying that scratching Mac isn’t obviously very shitty behavior. (and part of the reason Mac is emotionally avoidant is BECAUSE Dennis lashes out like this.) I'm just saying Mac is emotionally avoidant most of the time and Dennis hates it.