I've never jerked with another guy and it doesn't appeal to me. Male nudity doesn't bother me at all, but I also don't care to know what a male friend of mine's dick looks like and I see no reason to show him mine. As far as I know, the only guys that have seen me erect were participating in the same threesome.

But the circle jerk phenomenon you mentioned is pretty common and apparently quite a few straight guys have done it. It looks like I buck the trend here, but hey, you asked.