Late 70s I went to a nude beach with some college friends, 2 guys, 2 girls. We were all 18. Small beach, about 30 people all naked and older. We sat on our blanket, we talked the girls into taking tops off. They said we(guys) had to get naked first. We took off out shorts, we were both hard, embarrassing. The girls slipped off their bottoms. Minute later I was just semi hard, all good. We decided to walk to the water, I stood up, looked at our girls naked bodies and the other people all naked and I was full hard again. My friend was about half hard. Girls didn't say anything. I was very self conscious about everyone looking at my hard-on but as soon as my feet hit the cold water my dick went down. We splashed in the water for a few then went back to our blanket. My dick went hard to soft several times during the two hours we were there. I tried not to look at my guy friend but I did see him hard and soft. I was nervous the whole time but it was fun.
Late 70s I went with my then g/f to same beach. She was way into sex so she was into going. We get there, it's pretty crowded, we sat kinda close to an older couple, they were cool, said hi to us and chatted a bit. We were 19 they were probably 40-ish and good looking. We were enjoying the sun, walked to the water, splashed around then back to our blanket.
One end of the beach was secluded from the walking trail to the beach but about half the people on the beach could easily see the end. People would go down there and mess around. We saw a girl getting it from behind as she leaned against the rocks. Another rode her guy while he was laying on the sand. My girl wanted to go down there and have sex but we were both afraid. We looked over and the couple near us, she was holding his hard dick stroking it slow. I was hard, the guys wife just smiled at us. We walked to the end of the beach and I fucked her from behind. She loved it.