How does Mittelstaedt treat Kantorek? Why does he do this?

Mittelstaedt completely humiliates Kantorek, much to Paul's delight. He acts like this is a sort of payback for the way Kantorek treated him at school.

Mittelstaedt stops in front of him: "Territorial Kantorek, do you call those buttons polished? You seem as though you can never learn. Inadequate, Kantorek, quite inadequate--"

It makes me bubble with glee. In school Kantorek used to chasten Mittelstaedt with exactly the same expression--"Inadequate, Mittelstaedt, quite inadequate."