When I was in my mid twenties, I was having a one night stand with a random guy I had met. We'd sucked each other and I fucked him. At one point he was riding me when he abrubtly got off. No problem. I thought that maybe he wanted a break from being fucked and was going to suck my cock. But instead, he removed the condom I was wearing and than sat back down. I was shocked for a few seconds. Than, I admit, I hit him. I left him on the floor of his bedroom as I dressed and left. He didn't say or do anything. Guess he didn't want to make me any angrier.
But the one that I remember as my worst happened when I was a teenager. Nothing too horrible, but I still see it as one of my worst experiences. It was also one of my first sexual experiences. An older man had hit on me and asked to take me to a hotel. I was surprised that I had been propositioned (I was very young and very closeted) and I was surprised to hear myself agreeing. He had me hide in his car while he got the room. Once in the room, he began showing me pictures of his wife and kids. Seeing the photos, I realized I was about the same age as his son. Creeped me out a bit at the time. Then he pulled down his pants and grabbed the back of my head. I sucked his cock for less then a minute and then he jizzed in my mouth. Not a problem there, as I was wanting to taste his cum. But than he patted me on the head, told me what a good boy I was, and rolled over and fell asleep. And there I was, a fully clothed teen boy, on my knees with the most painful, raging boner I had ever had and a snoring man in front of me. I was angry. I thought of taking his wallet. I guess I wanted some sort of revenge. But I didn't take it. Just got up, walked out, and headed home.