I was living in Georgia at the time, and at work I broke my arm. It was my right arm, which I used almost daily to satisfy my needs.
I was going to move to another town, and asked if my brother could help me as I wasn't able to pack anything. He came over, and during the second evening we were watching TV. He started to ask me how I was doing things with only my left arm and hand, and I told him that it was quite difficult as I am right-handed. He then brought up masturbating. I told him that I hadn't tried since I broke my arm.
He pinned me down on the sofa, and started to unbutton my jeans. At this point I knew what was about to happen, and I could feel my dick swelling.
He slid my trousers, and boxers to my ankles, and started to jerk me off. It was the best feeling ever.
Once I was done, he undid his trousers, I could see the outline of his dick by that time. He took his dick out of his boxers and started to jerk himself off. After I had recuperated, and was erect again, we decided to measure our dicks, they were both the same length. He then kept on jerking himself off, while at the same time jerking me with his free hand. It was great.