Let's see, there was the one I just started anti-depressants and they had unexpected side effects preventing me from getting hard. It was a rather poor sexual experience.
There was the other, which is way more fun, where I befriended a women I was working with. She was lesbian and had a kid. Her last sexual experience with a man was when she was raped. Anyway, she invites me over and after a couple drinks we settle in to watch a movie and start fooling around. I go down on her for a while and then she has me move towards normal sex. Literally ten seconds after I enter her, she excuses herself and goes to the bathroom to throw up. She thought she was going to be okay with it, but had more of a reaction than she expected.
Eventually, she comes back out and apologizes. I didn't mind though, we ended up just cuddling watching the movie until we fell asleep. 10/10, would sleep with a lesbian again.
We stayed friends for a while, I introduced her to one of my other friends and she dated them for a while. We hooked up a second time a few years later.
There was another one that didn't understand her kinks or communication yet. She would say things to try and get me jealous. She would also constantly say no or stop during sex and then get mad or frustrated when I would stop. It ended up just being a little awkward, but we were young and dumb. Too young to understand discussing what she wanted before starting sex and agreeing on a safe word.