This happened just last week. I was at work and there is a small park and river next to the building I work in. We have dark windows on our building so we can see out but nobody can see in. One night I was looking out of the window, and noticed that a man was sitting at the picnic table, that is about twenty-feet from the window. I was the only one in the building, and with the dark windows he probably did not think anyone was there.
As I watched him for a while I noticed that he was rubbing the outside of his shorts, then his hand slid inside his shorts and he was rubbing his dick pretty good.
I have always wondered what I would do if I ever caught a guy jacking, I was about to find out. After a little while his head went back and it was at that point that I noticed that my own dick was rock hard. I figured I was all alone in the building so I whipped out my dick and started to rub at the same speed that he was. It didn't take long for me to shoot my load all over the wall in front of me.
Shortly afterwards he must have shot his load too because he just sat there for a while before putting his dick away. As I was cleaning up my mess he left the park and I have not seen him since but look forward to the time I can watch him jack and join him from behind the window.