I had a horse stalled next to my TB mare years ago, who was quite mean. I even put hotwire up so he couldn't reach into where she eats. Unfortunately her gate was right next to his stall, so he's lunge and bite her every time I took her out or put her away. Of course the owner thought the horse was a saint. Got so bad, that my tb actually punctured her hip bolting into the stall one day when he tried going after her again.
Had my Arab in several different pastures, and she was fine in the first two, but the last one, the TB mare who was the lead mare, would bite the crap out of my mare, leaving really large nasty bloody wounds on her body. My mare wasn't very dominant, but was quite quick, and had only ended up with the occasional bite mark (that I could see anyways), in the first two pastures, but every single day I came out, she had a new bite wound from this mare. It was annoying because they were so visible, and the owner didn't believe her horse bit other horses. Then a new young Quarter Horse got added to the herd, and the other horses started getting their tails chewed. Now, understanding herd dynamics, my mare being on the BOTTOM of the pecking order, none of the other horses are going to stand around and let her chew their tails, nor will she being the least dominant horse, want to get that close to the lead horse to do that. Yet, the bo (and owner of the TB) blamed my horse (who'd been in the pasture without incident for a couple months at that point), like a) I could do anything about it if it was, and b) like the low man on the totem pole would ever try that. I wasn't paying board, I was working it off, and we'd already kind of had a falling out, so of course she didn't want to blame the paying clients horse. Of course right after my horse left, they moved the Quarter Horse into the barn. I understood putting my mare in pasture, that she'd get the occasional bite, they are horses after all, but when the owner thinks their horse is so sweet, and would never do that, that's what gets on my nerves the most. Glad I don't have to deal with that person anymore.