Well, if you're serious about quiet, during sleeping hours that leaves Topre, silicone, scissor switches, cherry clears (since you're an M user, better than browns), etc. There's no reason you shouldn't use your M during the day.
I personally couldn't fall asleep in a room with someone typing on cherry browns without ear plugs. Probably the same for cherry clears, but since they're harder to bottom out on, I have this illusion they're a little quieter. I mostly recommended clears, because you're an M user, so you're used to force and clears have more force and tactility than browns (though of course, still without audible feedback).
It is a dorm, why doesn't this guy have ear plugs and noise canceling over ear head phones, if he's so sensitive? Unlike loud talking/****ing, noise canceling headphones can actually have an impact on typing noise.
Remind him that the library is the quiet place.