I've just got back from the gym and have to tell you of an experience that has changed my view about bisexual tendencies. I have always been straight and really not interested in men or their bits at all. I had been in the gym and just stripping off ready for a shower. Next to me was an older man, probably about 65, maybe 70. he was also getting undressed and as I walked towards the shower, he took off his pants to reveal the longest cock I had ever seen. his balls were also hanging down and looked huge. I probably stared a bit, as he smiled at me as we went to the shower area. I had my shower and was drying myself in the small corridor when he came out of his shower. It actually looked fatter than before, probably because of the hot water. Without any reason I can think of I started to get hard and I know I was staring at his cock. I was fascinated by the size of his balls and how low they hung. I covered myself with my towel as he openly dried himself, spending time drying his cock with his towel. I walked back to the locker area to get dressed and as his locker was 2 from mine, he also came back to the same area. He started talking to me about the gym as he again rubbed his cock with his towel 'drying himself'. He was definitely getting harder. My own cock was also beginning to rise as he looked at me and within seconds it was standing up. It was difficult to hide and he also made no attempt to hide his erection which although it had not got any longer, was definitely a great deal fatter. Luckily there was no one else in the changing room and he started rubbing his cock with his hand. I could not believe how sensitive my cock was and I copied him and started pulling back my foreskin. He stood next to me and took my hands and placed one on his cock, and the other on his balls. What was I doing in a public changing room touching another man's cock? I didn't care as I rubbed it. As I pulled back his foreskin, his very wet end was huge and I have to say I enjoyed feeling it in my hand. He told me to go quicker and within 30 seconds he shot 3 or 4 loads of cum onto my arm. what I enjoyed the most was the amount that he groaned as he came. As he regained his breath, he took hold of my cock and within 2 rubs had made me cum. My legs wobbled with the intensity of it and I shot a very large amount in one go onto the floor. Of course then common sense kicked in and I got dressed as quickly as I could, not even looking at him and left. The guilt I feel is tremendous, but the pleasure I got from it is overwhelming. I've told myself I'm not doing that again..........