A few months ago when I was visiting a class I frequent, the instructor referred to one of his adult students as "Fat Man." A few of the other karateka chuckled, but since the student is a good friend, I know weight - and trying to lose some - are big issues for him. OUCH.
In another class, the sensei is big on telling all his students that gender doesn't matter on the mat and that there are only karate students in his class, not males and females - but when demonstrating self-defense techniques, he is quick to jump on the "women are delicate creatures" bandwagon by insisting the females do techniques that involve raking or poking the eyes with our long, "fresh-from-the salon" fingernails (yep - he actually said that) that none of us have (because as martial artist, we can't make a proper fist with them) while having the males work on punches to the face. The reason, he says, is that most women don't want to hurt their hands by punching with their fists. Sexist OUCH.
Although he is now a third kyu, one of the kyus that came over from my old school to the new one still has a bit of difficulty with his some of his rolls, falls and kick placement because his first instructor (who was also my first instructor) didn't place much emphasis on those basics. Today in class, an instructor addressed the group after the kyu demonstrated a front roll to emphasize the importance of having a solid foundation of basics. "The color of your belt is only to show the number of years you've been training, really," he said." It doesn't necessarily tell you how SKILLED a person is." Unintentional OUCH.
Another sensei I've trained with is big on pointing out the errors in technique, which is a good thing. But although I know it's designed to make us all better martial artists, I gotta tell you that it's diffucult to hear "NOPE!" or "That's totally wrong" or "You're doing that like a white belt" over and over without feeling like you can't do anything right. Gut-wrenching OUCH.
I've seen the look on the faces of students when they've been put on blast in class and it is hard to watch. But what's even harder to watch is when the person dishing out the harsh words doesn't realize the effect what they've said has had. To them I say this: you may think it's helping build character/toughening your students up, but in reality, what you're doing is the verbal equivalent of bullying. That might be the way you learned, but perhaps the same is not the best way to train others.
In other words, whether you are a student, student teacher, sempai or head instructor, be careful with how you address folks on the mat. Maybe this anonymous quote sums it up best: "Keep your words sweet. You may have to eat them later."