I've got 2 takes on this.
The first has to do with a similar experience when I had I was living in Atlanta.
There were several odd things about the situation.
1. It was at an internet organized public game day at HOBBY LOBBY. (who just won the right not to pay for contraception coverage due to religious objections of the religious owners, challenging that part of Obamacare before the US Supreme court . this was about 5 years ago). There were families and children wondering by as we were in the modeling section. Some teenagers were playing with the other tables.
2. There were 2 women in my group. One was the GM. It was a few years ago, so the details are starting to blur, so I don't remember if both were lesbians, but at least one of them were. The open "butch" type. The GM and the other woman had played together before, and the non gm woman didn't have any problem with the GM's behavior, and also didn't seem to be aware it "should be" considered a problem.
3. The offensive behavior by the female GM was running a graphic gang rape scene (orc raiders with female captives. The PCs interrupted.)
My problems with this were:
A) it was a public game with non-gamer moms and children present.
b) hosted by an openly religious business that was friendly to gamers.
c) her job as GM was to create a scenario for a table of "all comers" strangers, some of who had never played before.
The Gm had basically failed her wisdom check, and had failed to consider that her usual "grim and gritty" play style was inappropriate for this setting.
While the game was going on, I didn't raise a fuss. I didn't want to draw attention to our table, or interrupt the fun the beginner at our table was having, but the other veteran gamer across from me and I had a silent conversation of eye contact, "I can't believe this" expressions, and shrugs as we agreed to keep our heads down. As the event broke up, I told him I'd handle it.
I contacted the event organizer by text and email and explained the situation and my concerns. He consulted with the GM, and though I wasn't party to that exchange, he informed me that she wouldn't be running games organized by his group any longer.
My primary concern, was that she was projecting a negative image of gaming to the public.
Some people, who might be just fine at running a fantasy game, just don't have enough awareness of what is, should be, or could be perceived not to be, publicly acceptable behavior, and what topics could be problematic and prone to make others uncomfortable. Many gamers are guilty of this, and more struggle with understanding different levels of comfort in private settings.
Your friend may just have this kind of social blind spot. (ever read Knights of the Dinner Table?)
My second take, is from loosing a friend ship due to my friend suffering from bi-polar disorder (aka manic depression). He was a nice, caring, diplomatic guy...until he stopped taking his meds. At that point, he simply seemed incapable of understanding , or perhaps simply refused to abide by, social conventions. He ended up loosing his job at the arcade for showing a pornographic drawing to children, the kind that only looks pornographic when you cover half of it, and then also thought the off duty officer who provided security would think it was funny.
He seemed to be always looking for the joke, and responded to any challenge to his behavior, however diplomatic, by getting more outrageous. This is, unfortunately, the most common response when someone is challenged for inappropriate behavior. (another is to be offended at you for being offended; like it is a "freedom of expression" thing for him.)
I don't know your friend. Maybe he has a personality disorder. Maybe he'll grow out of it, maybe he won't. Maybe he'll be diagnosed, maybe he never will. Maybe he'll someday get treatment, maybe he never will.
Now to your problem.
1) he is making you uncomfortable.
2) he is (perhaps) damaging the reputation of gaming by behaving badly in public.
I know you (probably) don't want to be drawn into "defense of the honor of gaming", but that is the situation. If his behavior is offending you, and you are being "offended for others" (the others who may hear his profanity and decide not to say anything despite being offended) then you need to remove something from the situation, either yourself, the other players, or the gaming site.
Perhaps you can
a)talk the group (not just him) into agreeing to rotate gms? (have someone else gm a 5e starter game to "see if we like it".
b) Arrange a different location (are you college students? you get access to public use rooms. this is part of your "Activity fees". I helped set up a college club that way. We got access to what ever classrooms were not being used, and could sign up to use the student center.)
c) discreetly talk to the other players, and challenge him as a group.
d) email him a link to this tread, my post in particular. "Hey man, some people think your behavior qualifies as a mental disorder." Maybe he will "get it" if he reads the thread. Don't hold your breath though.
