My two meanest teachers turned out to be the most influential. I didn't appreciate them all that much at the time, but I do appreciate them a whole lot now. Tough love is something teenagers don't really understand until it's too late I guess
It's wonderful to read about this sort of teacher. Everyone should have at least one such, in high school.
I was lucky enough to have had two such, one for general science, and the other for physics. Definitely both were "instrumental" to my education and to help solidify what I thought I wanted to do when I grew up. And I've been using what they taught me to this day.
Counter-intuitively perhaps, the general science teacher, who graduated with architecture degree from undergraduate school, ended up getting a PhD in ... art history! Obsessed with ancient Rome.