I was nude on a naturist beach on the east coast of Australia. There were a few nudists near me but I became aroused when I saw a lovely nude girl close to where I was sitting. Like most nude ladies on the beach her pussy was shaved. I didn't mean to get a slight hard-on while still on the beach but it happened to me regardless, man she was beautiful.
I needed to masturbate to reduce this powerful urge that had suddenly overwhelmed me. I did not want to do it on the open beach where I would be seen, so I went into the nearby dunes where I was fully hidden. I began to masturbate and had a strong erection. I was looking down at my hand stroking myself and getting ready to watch my cum shoot out when suddenly a lady's voice said, "He's masturbating Stan!"
What a shock! I was startled as I had been looking down and I hadn't seen anyone coming round a corner in the dunes. I thought I would hear someone before they could surprise me, but alas I was surprised.
When I looked up I saw a nude lady and a man. Flustered, I could only apologize and said that I would leave. The man, who introduced himself as Stan, said "Don't leave. My wife, Jenna, and I would like you to continue what you were doing. We'd like to see you finish yourself off."
I was really surprised at what he said and I asked "Do you both really mean that?"
"Yes, of course. We want to watch you do it."
Jenna then said something to the effect that she'd never seen anyone other than Stan masturbating and she wanted to see me doing it, providing that I agreed. So both of them, total strangers, wanted me to continue until I ejaculated. Having got close to cumming before they arrived I decided to do what they (and I) wanted. My erection was slightly reduced because of the shock I'd had but I soon got it fully up again as I stroked it. Another surprise.