I've had a few jo buds since I was a teen(am now 60).
My longest running bud was a guy I had known for about 10 years and we both went through divorces at the same time.(This was in the late 70's.) We shared an apartment for about 3 years. We both had plenty of females in and out of there, but I also knew that he jo'd on a regular basis and he also new that I did. One thing led to another and we started masturbating in front of each other watching a porno one night.
I couldn't wait and go off to my room as I would usually do, pulled my cock out, pumped it and shot my load. After I came, he pulled his out and did the same. After this, we would watch pornos together 3 or 4 times a week and jo whenever necessary.
We've both remarried, he's moved to Atlanta, and since have had no contact.
I don't know why, but like some of the other posters, I've had more fantasies of mutual jo sessions with guys for the past 5 or 6 years. I don't want to jo with total strangers in a video booth or park, etc., I'd rather get to know the person first. Many of the guys that I've IM'd seemed to be all for it until the time came to meet. All have been no-shows.
Since I know what its like to jo with another guy (not just teen wanking), my fantasies are maybe more real than some of you that have never shared the moment with another man.