I haven’t experienced bullying myself, but rode at a barn that had quite a few instructors with a widely diverging approaches to teaching. :: ahem :: One in particular should not have ever been allowed to teach small children. Nooo patience and lots of yelling. It was one of those “should I take the parents aside and recommend the instructors at the barn who are actually GOOD with kids?” situations. I didn’t, because if that had gotten back to the barn owner, my ass would have been toast. But this person was not a BNT and therefore there seemed to be a limit to what most people would put up with. This person didn’t seem to have a steady client base so either the kids/parents wised up, or the kids lost interest in riding. No idea how that situation is progressing as I’m no longer at the barn. And I didn’t dislike this person, outside of cringing if I was having a lesson at the same time as they were teaching.
My current instructor is… blunt like a hammer. I have definitely heard “Oh my god. What are you DOING? No, no no!!!” And I also got the “Well, that was a nice HUNTER round” comment from her. But in context it cracked me up and her next comment was “do it again, with more forward.” (and I also believe it was a jab at hunters – sorry hunter peeps – as much as it was a comment on the need for more impulsion 
But I don’t feel bullied or belittled. I firmly believe that she sees potential in people and gets irritated when they don’t make the most of it. In fact, when I rode like crap – maybe not crap, but certainly not WELL – this past Sunday, I felt like I’d let everyone down (my horse, her, and me).
I have not clinicked (cliniced? How does one spell that?) much and have little experience with BNTs. The worst I’ve experienced is “inattentive because you’re a beginner adult rider who doesn’t have money to spend.”
But if I were to define bullying in this context, I would say the following CAN qualify.
- Personalizing criticism, eg, criticism includes commentary on general intelligence, fitness, or body size (what are you, stupid?)
- Witholding praise or criticism
- Comparing riders to one another (look at Janie, she got her horse straight to the fence. Why can't you?)
- Unbalanced criticism, far more negative than positive (if there's not a lot positive to say, acknowledge what the rider is struggling with)
- General hostile or passive-aggressive behavior - eg, the "silent treatment" or refusing to acknowledge someone before a lesson/after a lesson/in the barn
- Also under hostile behavior is the "talking about you to others in the vicinity and pretending that they don't see you/aren't aware that you're there)
Sometimes it is a “I know it when I see it/experience it” thing; sometimes it isn’t bullying, it’s personality styles that don’t mesh or humor that doesn’t translate.
Actually, I shouldn’t have bothered to type any of the above: See below, taken from this site:
Signs of workplace bullying
The following signs of workplace bullying are adapted from research from the State University of New York and Wayne State University. While some of these behaviors may be isolated, if they form a pattern over time and are extreme, they may indicate workplace bullying:
Being left out from work-related social events
Coworkers storming out of the work area when you enter
Others regularly arriving late for meetings that you call
Being given the “silent treatment”
Not being given the praise you thought you deserved
Being treated rudely or disrespectfully
Coworkers refusing to help when you ask
Spreading rumors about you that aren’t true and that nobody denies
Being given little or no feedback about your performance
Others responding slowly to requests that were important to you
Being yelled or shouted at
Receiving put-downs about your intelligence or competence
Your telephone calls or other communications are ignored
Your contributions are ignored
Someone interferes with or sabotages your work
Being the recipient of mean pranks
Being lied to
Being denied a raise or promotion without a valid reason
Being given bigger workloads or shorter deadlines than coworkers
Being accused of making a mistake on purpose
A coworker throws a temper tantrum when you disagree with him
Being put down in front of others