The whole "soy" thing came from Bro-Science that alleges that ingesting too much soy lowers your testosterone and fills you with estrogen, making you a girly man.
I don't think there's any scientific evidence to back it up, but there's a lot of anecdotal evidence, being that a lot of guys on social media that rant and rave about how much they love soy products all look like this and make this same horrible open mouthed "smile."
Then you have stuff like this that doesn't exactly help the case:
I am not in any way saying there's any evidence about the soy/estrogen thing....but I DO think the "soy face" seems like a very real and eerie phenomenon.