By accident, I saw a man return from work and masturbate. I masturbated too, watching him.
One afternoon I was performing a survey on an unfinished building that had been deserted for over a year on a hill in our city. It had an open back wall of the basement that looked to other houses across a ravine. Buildings like that make me want to masturbate, but then I saw movement in the big windows of a house about 100 feet away.
I watched, and a man was obviously just returning from work. Then, amazed, I saw him start to strip off his clothes. When he was naked, he disappeared and came back with a full erection and his penis in his hand and was masturbating walking around the room and looking out the window.
I was dumbfounded and stood watching. He sat down and was edging, and then strode around the room more. I got turned on watching, and pulled down my pants and began stroking myself with my eyes on him. I was getting very aroused when suddenly he saw me and in an instant ducked down out of view.
I felt horrible!! I was really confused, and didn't know what to do. I thought of going around and finding his door and apologizing, but didn't. Instead I just hurriedly left. That night, I began to think, though. It was really a turn on seeing him!! So...the next afternoon I went back. This time, I hid myself.
Sure enough, he came back, and before he stripped, he went to the window and looked over, carefully. Then he got naked again, went to the bathroom (for lube, I figured out) and came back masturbating. I began to stroke, too, from my hiding place.
Then, it occurred to me that, the way he looked over toward me, perhaps he was really hoping to find someone. Perhaps, during the night, he had also been excited by what happened. So I moved out from hiding, just a little. Then a little more. And more. Then he spied me! He suddenly stopped jerking, and then, after a breathtaking moment, resumed. My heart was pounding. I started stroking again. He was full on in the window.
I was fully dressed, and now I stood up and pulled my pants down, standing, watching him stroke, and being watched. It was SO hot! Then he came, a big, muscular orgasm, and disappeared!
The next day, I went there again, and saw a note where I had been. It said, simply, I totally got off on you, but please don't come here again. Thank you. And so I left, with awesome memories of that afternoon.