This term has been popping up a lot recently all over the Internet. Despite sharing a name with an internationally famous Asian restaurant, it's typically a pejorative term. The meme is based upon a fake-news report of two decades ago claiming that consuming soy products causes men to acquire feminine characteristics. The revival of the myth and meme have been attributed variously to Internet crank Mike Cernovich or White Supremacist James Allsup.
The Urban Dictionary explains that the term is "slang used to describe males who completely and utterly lack masculine qualities. This pathetic state is usually caused by an over-indulgence of emasculating products and/or ideologies."
Seriously? Well then, here we have the evidence that the term is actually politically-based. Nonetheless, the article continues:
"The origin of the term derives from the negative effects that soy consumption has been proven to have on male physique and libido."
Like the body-builders who use Soy Proteins, I suppose...
"The average soyboy is a feminist, nonathletic, has never been in a fight, will probably marry the first girl who has sex with him and likely reduces all his arguments to calling all of his opponents Nazis."
The same author who concocted this definition also wrote an entry for Urban Dictionary under the title "TSNB" which he informs us stands for "Typical Sand-Nigger Behavior." The reader can figure this one out for himself; it's not unlike Hitler's definition of Arabians: "half-Jews who are only fit to be whipped."
It's surprising that so few have noticed a couple of obvious flaws here: one that Asia consumes most of the world's soy and has produced most of the world's martial artists. Two: that it stands to reason that transgenders would consume soy instead of costly estrogen treatments.
Concomitant with this Conspiracy Theory is one that asserts that consuming onions is the effective way of countering the allegedly negative effects of soy. One bozo at 4Chan claims to have drunk a cup of raw onion juice. Calling it a "trying though masculine experience" he doesn't tell us unfortunately what type of onion he used. This caused considerable debate among Manosphereans as to the efficacy of various onion strains.
Frankly all this talk of soy and onions has made me hungry for a Big Mac.
IOW, don't make your diet into some grand political statement like these losers are doing. Eat what you enjoy eating and what benefits you. The term 'Soy Boy' is nothing but more anti-male shaming-language and should be treated in that spirit.