A bunch of weird woman-hating incels co-opted the "redpill" language. I first saw it on /r/redpilll but I'm not sure that's the origin. It honestly probably emerged from gamergate. Essentially, they rejected the notion that being a "nice guy" gets you anywhere in life. They promoted shit like "negging" instead, which was the idea that women will find you more interesting if you insult them. There was more heinous stuff than that, but you get the idea.