Years ago, I used to go to a summer resort (non-nude) which had a big pool and a jacuzzi-type hot tub. I was in the tub by myself when couple of hot girls in bikinis got into the tub with me. Watching their sexy bodies, I started to get horny and took advantage of the bubbles from the jets to start to rub my cock through my loose trunks.
The girls left and I got even hornier. I let my stiff cock peep above my waistband and rubbed it harder. No one could see thru the bubbles, so I loosened the strings in my waistband and eased my trunks down. Then I took them off completely. I was nude in the hot tub and jerking off with people all around but completely unaware.
I couldn't hold back any longer and I orgasmed my load of sperm into the water. My rope of cum floated around, twisting in the turbulent foam until it gradually dissipated. I got my trunks back on and climbed out of the tub with my legs shaking. It was risky but worth it!