At the age of 18 my best friend, John, lived across the road from me. I spent most of my free time at his house, since his mom worked all day and we could get up to all sorts of mischief. His step sister, Rozanne, was 21 and in her third year at university. She was a rather chubby girl with curly dark hair and often grumpy. She never had friends over, and she spent most of her time in her room. Rozanne would sometimes sneak up on us to spy if were smoking, which would then get us into trouble with John's mom. We were always on the alert in case she crept up on us. John lived in an outside room attached to the garage, with his own bathroom.
We often listened to music on John's hi-fi, and enjoyed just hanging out together. One afternoon after a sports match we were hot and sweaty. We went to his room and decided to have a shower. We both dropped our clothes and stepped into the shower.
We were joking around as we often do, when John said, "Lets see who has the largest cock!" He closed the taps and held up his large limp dick on the palm of his hand. It was all innocent fun, and we faced each other and held our dicks close together. We both have large ones with long foreskins. I noticed John's cock suddenly getting hard, and I had a strange type of erotic feeling that instantly got mine growing harder too. We were laughing about it, and John pulled his foreskin right back exposing his large, mushroom shaped cock head. Suddenly he grabbed my now rock hard cock and pulled the foreskin back. It was the first time anyone had ever touched my cock. It was such an intense feeling that I gasped aloud.
He let go of my cock and laughingly said "let's have a cock fight!" and grabbed his cock at the base and began slapping it against mine. I grabbed mine too and slapped his, our cock heads and shafts connecting continuously with hard impact. Although we were laughing and fooling about, after a few slaps I started feeling my cock and loin area warming up as if I was about to cum. I let go of mine, but it was too late. John gave it a couple of more slaps while my body started shuddering. It was a very embarrassing moment, perhaps making it even more erotic in a strange way. My legs started shaking and I shot out several spurts of cum. The strong bursts hit John against the belly and there was even some on his cock and balls! I thought that he was going to taunt me or be disgusted, but it obviously turned him on too and he stroked his cock hard a few times and I realised that he was cumming too. He squeezed his cock hard and shuddered wile a huge load of white cum shot out, this time hitting me on the upper thighs. It felt hot as it trickled down my legs.
After that we did not say much, just showered again and I went home.
The next day after school I went to fetch a book from John's house, when Rozanne met me in front of his room. As usual I just nodded and tried to walk past her when she grabbed my arm. "Mike, we have something important to talk about," she said. "Come into John's room!" She was always a very bossy type of person, and the best way to handle her was to obey her, even though we always taunted her behind her back.