My peak public sex experience was with a buddy in Central Park. Was early autumn, still very warm out, and we went to the Park for the express purpose of fucking. He wanted to show me the rambles, and fuck me there. I wore a pair of jeans with the back seam ripped out, so that if I was just walking down the street, they would look normal, but if my bud wanted access he could just pull the fabric apart and go.
We met basically at twilight. Sun had gone down but still pretty light out. He pulled me off the path (can't remember exactly where, but was around 74th street? Maybe?) and started entering me from behind through the jeans. I was really getting into it and then looked up and a guy was watching us. This startled me but he held onto me and told me it was okay and kept fucking. The guy watched for a while and then left, and then we decided to move to a different location further into the park.
Here he decided I needed to lose the jeans. I was already shirtless and wearing flip flops, so now I was totally bare-ass naked and barefoot in Central Park, and he stepped in behind me, I was semi-bent over, and he started fucking me. And fucking me. And fucking me. It was NOT a quickie.
A guy started watching, and he took his cock out and started jacking as he watched. As we were in a standing position, I was in a perfect position to take his cock in my mouth when he approached us and put it in my face. I sucked him as my bud was fucking me. Nice cock, about 7" uncut. I think he got spooked because he didn't let me finish him off. He pulled out and went on his way. We continued to fuck. His cock did not leave my hole for over an hour. And I didn't have a stitch on. Neither did he. He finally came in the condom in my ass, and then blew me and I came in his mouth.
I put on my jeans and my flip flops, and he dressed as well, but as we walked out of the park and back to his place somewhere in the 70's (I think 76th?), he fingered my hole through the hole in my jeans. As we were waiting for the light to cross central park west. He had his hand on my ass, and was discretely fingering me through the torn-out seam. He continued to do it as we walked across the street in front of the cars stopped at the light.
We had a few other adventures as well, but this was the best one.