[He's standing up for himself, that was unexpected. Kanda hadn't had any real interaction with Gongenzaka previously, but assumed he would be an easy target because he was always so damn polite to everybody. Challenge accepted.]

It's Professor Kanda, you impertinent little shit! Your eating habits are my concern because you're setting a bad example for the other students with your gluttony, Gongenzaka.

[He glares the kid, very much with malice.]

Your backtalk is not appreciated. How dare you be so insubordinate and disrespectful.

[He's the kind of teacher who hates you for no reason other than that you exist.]