I noticed increased frequency of posts in places like r/rpghorrorstories, that describe a situation where the player brings a tiny veiled or just a shameless copy of a popular fictional character - Sokka, Scanlan, John Snow, Walter White - except "more based" or "less of a cuck". What follows is a story of the player doing some horrible manosphere shit.
I know that a lot of posts on places like these are fake, but in this case I kinda hope they are. Or that it's all the same guys at different tables. Either is more comforting that an idea of an army of incels trying to rp their extremely toxic fanfiction on the table.
So ironically, I came here immediately after closing down Twitter, where I saw this in one of the trending tags. Transphobic rather than alt-right, but the overlap between those two groups is nearly 100%. This kind of thing is apparently (based on other replies) not how the term originated, but it's certainly how the term came to be popularly known.