Taku isn't the most respectful and polite student around, so there's a certain teacher who gets constantly annoyed with him and lectures him endlessly, even for minor misbehaviors. It's probably 70% Taku's fault and 30% overreaction on Sensei's part. :'D
Comic transcript
Taku: "Plus, I could do without getting lectured by Sensei AGAIN."
Kei: "Alright, then. Time to get the dustpan."
Serika gets up and starts walking out of the room together with Kei.
Serika: "And I seriously need to wash my face..."
Kei: "Yeah..." chuckle
Serika: "Are you coming with us, Taku?"
Taku: "Just a sec."
He watches the two leave.