To me, i think the mole is only the surface of the reason, he more likely to be shocked when he yelled rude things to the girl he liked. So he covers his mouth so he avoid speaking like that to others (ex: he want Saikawa to keep secret the fact he yelled at him in the infirmary or he isolate himself in class). I get his feeling somehow, when i was young i said something which i only mean to be a joke but that friend understanded diffrently and had bad thought about me since then. I could feel that and i become untalkative and hard to open myself to strangers (sr for being so long ): )
Yh he had a problem with him talking about how he shouted in the classroom so its defo less to d ok with the mole and more to do with him speaking
I thought the reason he's wearing a mask would be something more interesting.
I was also teased for the mole I have in the same place and swear like there's no f-ing tomorrow. Like hell I'd wear a mask just for that.