When did ALL-CAPS type become YELLING?

Mrs. Winslow's ALL CAPS Soothing Syrup, 19th century. History of Advertising Trust/Heritage Images/Getty Images

You've seen them before, whether in a forwarded spam email, a strangely passionate Facebook post or a weirdly emphatic comment on your favorite website: THE DREADED ALL-CAPS TYPER. But where does this practice come from? How did everyone agree that typing in ALL CAPS means you're yelling at someone via text? Tune in to... FIND OUT.