It's not so much of question of jacking off "with" other guys, as it is a question of masturbating in a setting where other guys can see / hear what you are doing. Obviously there are some very sexually conservative guys out there, but I would say in general, by the time guys are in their late teens, we're pretty aware and comfortable with the fact that we all masturbate a lot or have masturbated at some point. So, I don't think many guys would be too shocked about masturbation in an all-male setting like a dorm: we're all guys and we all can understand the urge to masturbate. I've been in hostel dorms where I've seen or heard guys masturbating and it was a non-issue. One time in particular, a guy brought a girl back to the quad male dorm late at night and they had full on sex, even in the dark I could see pretty well everything, it was a hot summer night and we were all sleeping without blankets. It made me really horny so that the next morning I was stroking my hardon a bit, and the guy in the bed across from me was lying on his back checking his phone and then turned over to face the wall. I didn't get the feeling it was because he was uncomfortable, but just because he understood and wanted to give me some sense of privacy. Yeah, masturbation is more ok in certain situations than in others, but in an all-male, adult or young adult setting like a hostel dorm, I don't think anyone is going to be that uncomfortable with low-key masturbation.