There is no strange illness responsible for the constant, unsettling grins you see at baseball games and among the Good Morning America audience.
It's really a promotional piece for an upcoming horror film titled Smile.
PopCrush reports that on Friday, September 23, a group of individuals dressed as the devil appeared at three Major League Baseball games .
As it turns out, it's a promotional tactic for the upcoming film Smile, which releases this coming Friday.
It is most likely why so many people were wearing T-shirts that simply said "Smile."
Whether officially sanctioned or not, the effort seems to be having an effect, at least in the online sphere (and on baseball camerapeople).