Ancient idiom that was revived on September 12, 2021, when a resident of Massachusetts used it in response to an incredibly dumb comment by his friend.
Person1: “Bro, if the vaccine works then why are so many people still dying?”
Person2: “Dude, your forehead is showing again.”
Person2: “Dude, your forehead is showing again.”
by daHoffer September 12, 2021