I’m straight but I think all men are fascinated by other men’s penises and men’s sexual activity. In my teens I got naked and masturbated with and hand jobbed with other boys as we ogled straight porn pictures of naked women. The same when I was with my climbing group in a dormitory and the porn (Penthouse, Playboy, Mayfair, Fiesta, Escort mags) and girls’ panties came out, then the erect cocks, then the semen. We were all as straight as they come but masturbating together added a level of excitement.
Never a group of guys, but I loved jerking off with a neighbor friend of mine in my early teens. It went on for almost 2 years until we both started looking at girls. That early experience brought out the bi side of me over the years as I realized there is still a lot of pleasure to be had amongst like minded fellows.