I have... by my old TRAINER. I was living out of town for four years, and when I moved back in the area I wanted to get back into lessons so called her up. She has been out of horses completely for a couple of years, but was willing to teach me. The lessons... weren't quite what I remembered them to be. Not long into my last lesson my horse wasn't being quite "right" (I think he was worked up by something going on outside, and I was a bit upset by the lesson and my trainer thus far) and she asked if she could hop on him for a bit to see what she could feel. She's ridden him countless times during lessons, so she hopped on.
Boy, it was a disaster. The horse did nothing wrong, but she got on and started kicking and jerking him around. Kicking him, and I would go so far as to say see sawing him to get his head down. Jerking his head to the inside and kicking him around. I was getting to the point that I was about to ask her to get off when she was announced that she couldn't figure out the problem. I finished that lesson, and since I was just starting school in a week or so I said I was too busy for lessons.
The worst part about this? My barn is usually very quiet with almost no one there, but EVERYONE was there today. The barn manager and her sister, farrier and his wife, another boarder and her daughter, the barn owner's daughter, and a friend of mine that also boards at my barn. I was absolutely mortified, and was desperately hoping that no one was watching and thinking that riding was what I sought out and that was what I called a lesson. Conveniently just about everyone was paying attention to the horse shoeing during that time period, and I explained the situation to the barn manager and my friend...
I would never be embarrassed by a dead beginner, provided that they weren't doing anything dangerous. Everyone has to start somewhere, and who's to say that you weren't being laughed at when you started riding
I have an infamous picture in my archives from when I first started riding. I was in "two point" going over some trot poles with basically a hump back, puppy paws, totally pinching with my knees, and my toes pointed at the ground.