I used to have a bad habit where I bit my arm whenever I got overstimulated from my autism during my teenager years. So this is how this scenario came to be;

Jongwoo:

Are you a cannibal..? At this point he is starting to feel HE is the weird one! Is everyone a cannibal and he doesn't know?! But you argued it's just a way to vent anger, to which he blurted out "what kind of fucking solution is that?!", only to realize how harsh and true disbelief that was so he mumbled a sorry awkwardly before telling you different ways you could vent anger and sadness.

Moonjo:

Good! Excellent! Now he doesn't have to spy in your mouth at night anymore, he can just see the teeth's shapes in your arm. He will even tell you; "How sad. Didn't break the skin." Will do things on purpose to anger and overstimulate you to the point you have to bite.

Junghwa:

It worried her greatly, angered her as well as it means you don't value yourself as should be. Both had a big argument due to this.

Though once her irritation died down she bought you a silly gift: a chew toy.