I guess nobody knows how it really started. There was a guest on a show, some write for the times or wapo that gave a brief history. I think the general consensus is that it applied to those weird stories (often right wing targeting the left) that would get shared on social media and broadcast as news without any real credibility to them. Can't think of any specific ones, but you know what I'm talking about. The weird uncle forwards an article that sounds possible, then it gets picked up by others. You are smart, so you look at the source, scratch your head and don't forward it.
But they are more believable than say 5 years ago because mainstream media is so quick to get stories out, they don't do a good job of researching them, so they to are guilty of spreading fake news, but not intentionally. Well, at least most of the time. So the label sort of fits in well.
I know some people who seem intelligent, but they do not read regular news period. They get all their news from alternate media. These are people who for 5 minutes are pretty cool but then they get comfortable with you and the topics quickly devolves into how Lyme disease is covered up by the gov't or attributed to other more popular diseases, Vaccines are not just dangerous in some instance, but designed to control population, GMO is designed to sterilize the population, just like BPA that leaches into water from water bottles, and chemtrails are real. Sad part is they don't even how realize how stupid they sound.
Here you go, a perfect example of fake news as originally called out.
http://www.naturalnews.com/ Check out this article on how the Feds manipulate the only legal source for marijuana research.
http://www.naturalnews.com/...a-look-so-weird.html or how dental fillings made of amalgam are killing us.
http://www.naturalnews.com/...ect-your-health.html
"In the world I see you are stalking elk through the damp canyon forests around the ruins of Rockefeller Center. You'll wear leather clothes that will last you the rest of your life. You'll climb the wrist-thick kudzu vines that wrap the Sears Towers. And when you look down, you'll see tiny figures pounding corn, laying stripes of venison on the empty car pool lane of some abandoned superhighway." T Durden