Although this is likely outside the scope of this subreddit, I don't really know where else to ask.
After not seeing a cousin of mine for several years, he returned to my state with my aunt today to visit my family.
Essentially, he has become a walking caricature of the standard gamergater / internet shitlord, having no filter at all whatsoever, saying that "he loves hitler jokes", saying shit like "I prefer hitler to stalin" and "hitler is my hero" when I showed him a socialist meme, thinking that it's appropriate to laugh at a song written by a jewish person in a contentration camp for no reason other than "imaging him scratching help into a wall", describes himself as a "meme", says that he is "cancer and AIDS", and thinks that all feminists are feminazis and that he's a "meninist".
When I tried to impart to him that I was linked to 4chan when I was 13 and that all it did was stunt my development, he spouted some bullshit meme about how I was "merely born in the memes, I was raised by them", and that /b/ was better at some point in the past, completely missing the point entirely. He referred to me as a "normie" unironically.
He's evidently fallen in with alt-right bullshit and is trying to become a professional e-sports player.
My aunt, while she is a wonderful woman, thinks that it's fine that he's making "jokes" and that it's not as serious as it is.
Luckily, she knows that I've been around technology my whole life, and I believe that I have a unique opportunity to get her to understand that this isn't a joke or a phase, and that he's legitimately getting himself deeper and deeper into a hateful echo chamber as time goes on.
Can any of you please help me form a plan of attack to explain this to her while she's still in town so that we can reach him on this?
I don't want him to be stunted socially and emotionally into his early 20's like I was. I was lucky enough to snap out of it when I started to try to understand what people "were whining about" on ShitRedditSays, but I fear that he won't have that same opportunity.
Any links or help that you can offer me would be appreciated, as I don't want to have to go at this alone, and I genuinely want to help him before he's so cemented into this that there's no helping him.
Thank you in advance.