I had to put my mare in my dad's gelding's stall, and the gelding in my mare's stall, as she was injured, and she had a bigger stall and was starting to try and use it as an arena when she was supposed to be not moving much at all. Well they had a paint tb cross pretty big 5 year old gelding in the stall behind hers, and she kept teasing him. She was horrible when she was in heat, stopping at certain geldings, and refusing to move even if I smacked her with a crop. Talk about embarrassing, squealing mare, squealing gelding, and an inability to move said mare led to some awkward moments. Anyways, back to the stall, she'd tease the gelding, then he'd try to mount her through the pipe panels, and she'd start squealing and kicking, totally confusing the poor gelding.
Same horse, I had to warn people about when she was in heat, because she'd squirt at anything behind her, people included, so I had to make sure that people gave her a wide enough berth so that they didn't get squirted on. I was so embarrassed, I was in high school, and the fact that my mare would squirt at people (the only one on the farm), and I had to warn people about it just weirded me out so much.
I was told by someone I know, that they tried breeding one of their TB mares, and she kept not taking, so they finally did a really in depth breeding exam, and found a mummified fetus in her womb. Apparently it wasn't causing any problems other than keeping her from getting pregnant, so they opted not to do surgery, and just leave it there. No idea if it's really true or not, but just weird.
And last one, there was a stallion at a place I used to ride, he was 5 or 6 at the time, and he could be kind of aggressive with most people, but we had reached an understanding before I even knew he was a stallion. I walked by his stall, and he tried to bite me, so I smacked his neck, I was still fairly new to the barn, didn't know the horse, and never checked to see if he was intact before, and as I had to go by the stall, and had no choice, I decided to let him know it wasn't okay to try and bite me. Well most people had just jumped out of the way, he's a stallion, so they had the mindset that they couldn't correct him for some reason, so he was totally shocked when I did something. Well he never tried biting me again, so I started stopping by his stall and saying hi on a regular basis, as he didn't get a huge amount of attention. Well one day when his owner was there, I was petting him and talking to the owner at the same time, and the horse ended up masturbating while I was petting him, and when he was down, the owner was all like "well I guess he really likes you! That's good". I started avoiding the owner after that, it was just too creepy for me, though I still said hi to the horse, and he didn't do it again thank god.