This happened when I was a teenager in high school. I am by no means gay, but I do enjoy a mutual jerk. My geometry professor really got my attention; he was a great teacher, plus he was about 6'7'', in his mid 40s, and in great shape. I am not a model student, so he (lets call him Mr. Duncan) lets me come to his house to design a geometric garden for extra credit, with the correct angles and stuff.
So I go there one friday after school (he lived right next to the school) and I planned this garden. He helped me, making sure I got it right. We finished the garden at about six, and I had a meeting at 6:45. We were both pretty sweaty and definitely dirty, so I asked to use his shower so I could go to my meeting clean. He said sure, so I go in and strip my clothes off and start a shower. He knocks on the door not one minute later saying that he forgot that he had to get ready too, and asked if we could share the bathroom. I said 'Sure, why not', and he came in and got ready.
Well, as fate would have it, I got out of the shower at the same time Mr.Duncan pulled off his boxers, leaving us standing face to face naked. I'm not sure who went first, but we both had raging hardons. Mr. Duncan was like 'Well, there's only one way to make these go away' and reaches for my cock. At the time, I was about six inches long and pretty thick with a little pubic hair; he was at least eight inches hard with lots of pubic hair. So he starts jackin me off, and I do the same to him. This was the first time I was ever in a mutual, and this guy was a pro. I climaxed first, sending my cum all over his furry chest. He cums soon after, and then I finished getting ready.
Needless to say, I passed geometry with flying colors!