Kind of crazy how a teacher puts up a barrier that reflects magic back to the caster. Like, don't you think that you might end up indirectly killing a student AND be easily identified later by the principal or other school personnel who most likely understand magic as well or even better than you?
Never seen this trope, have you?
Yes, they're that stupid. Yes, they're annoying. and no... they get Recycled as Minor
Annoyances Villains regardless of what they do, because the author needs
some form of Antagonist. Lazy Writing using Tropes By The Numbers 101....
There's several ( generally less serious..) Manga dialling this up to 11, and then breaking off the knob.