IMO, this is worse than things like up all hours of the night and even drugs. It’s a legitimate gripe worse than a “minor personality difference”. No one needs to put up with emotional abuse and bullying which is what this is if the roommate is making derogatory comments about your son’s personality and intelligence.
It needs to be dealt with but the first step in doing so is asking for help - the RA and the counseling office. ASAP.
It’s likely your son will encounter other emotionally/verbally abusive people in his life at some point. It’s a good life skill to learn to deal with it.
I agree with most of the other commenters. I’m not seeing mental instability and danger here.
FWIW, there are so many students who don’t get along with their roommates. My D and her first year roommate didn’t care for each other. D spent a lot of time not in her room, and I think the roommate did the same. . It wasn’t great, but it wasn’t horrible and she got through it. I fully agree that your son needs to advocate for himself and just get through this. My D is a conflict avoider but her way of resolving it was to remove herself from the awkwardness s much as possible. Not what I would have done, but it worked for her.
This is how I read it, not that the roommate is a bully but that the roommate is socially unable to fit in with others so wants OP’s child as a friend. Wants to do everything the other student does, follows him around, wants the same friends and is afraid if he (OP’s child) makes other friends then the RM will be left without anyone.
I work at a university. We would take this, especially the personal comments, seriously. It’s not an RA issue. RA issues are a difference in preferences for thermostat settings and similar disagreements. It sounds like the roommate is creating a hostile living environment.
Your son should be documenting what the roommate is doing/saying (dates, times, witnesses). I’d recommend seeing a counselor on campus for suggestions on dealing with the roommate, then go to the Dean of Residential Life with his documentation and tell them he wants a room change. Start creating a paper trail.
In the meantime, he should live his life. Invite people over, go to events without explaining his schedule to the roommate, and quit giving in on things he doesn’t want just to avoid conflict. The roommate can only run his life if continues to let him.