Get ready for the dumbest shit ever.
Basically, alt-righters, Trumptards, and other not-good people call liberal men "soy boys," because apparently soy lowers testosterone, making them emasculated degenerate losers, and only sensitive feminized men are leftists (The ingredients in soy lead to pro-Communist thinking, I guess). Basically, eating soy doesn't make you a "real man" or some shit.
It's funny, because as someone who occasionally leans towards socialist ideas in his politics, I think soy is nasty as shit.