I've noticed for a while that Yayoi likes to give certain quirks to characters when they're nervous or stressed
The most obvious one being Arata and scratching his neck (I think he usually does it during high stress)
There's Yoake who taps his fingers (something Onoya notices)
Hishiro clenches her dress (or the hem of her shirt)
And then this chapter it's Ohga with his piercing
Two of them have a specific story behind them which is really interesting
If there are any more I'm missing, then feel free to mention it