I'd like to think Michael uses demon face reinforcement outside of sex too. Maybe you mouth him off just a bit too much and he grabs you by the arms and pulls you close. Demon face comes out and he says "remember who's in charge. Remember who decides if you cum or not. Now run along." And shoos you away (I'm more of a softdom!Michael so this is probably in front of the cooperative and at home he let's you cum anyways.)
This is so Michael I’d say it’s practically canon! It’s the perfect little warning and he only uses it when he’s genuinely irked as it can spook you when caught off guard.
One time he asks if he can make love to you with his demon face on, his the once because he doesn’t want you to fear him if he had to display it for a while. You agree and he’s so careful as you inspect every crack and crease, wondering how he can be so perfect and so ruined at the same time?