According to Wikipedia, "A tin foil hat is a piece of headgear made from one or more sheets of tin foil, aluminium foil or similar material. In theory, people wear the hats in the belief that they act to shield the brain from such influences as electromagnetic fields, or against alien interference, mind control and mind reading. The idea of wearing a tin foil hat for protection from such threats has become a popular stereotype and term of derision."
Ohhh, so that's what it means. I had heard the term bandied about for years but was never sure. The world is increasingly unstable, with natural disasters such as the midwest tornadoes and the China earthquake; man-made disasters such as the Florida fires started by an arsonist and the California fires difficult to put out; the dollar's decline and US likely economic collapse; food price increases; and stocking up (or 'hoarding' if you are a tin hatter). If all that's not enough to make you think the world is coming to an end, I don't know what will.
Some tin hatters go deeper. There's the 9/11 Truthers, the "New World Order/Illuminati" conspiracy theorists, the "Whole World is Turning Into a Police State" conspiracy, or "Obama is a Secret Muslim ," and "Reptilians Run the World" conspiracies. These are real conspiracies that people believe.
But...when mainstream newspapers publish articles about grandmotherly women selling everything and living in survivalist mode, and actually include the phrase: "maurading hordes" then it's time to rethink things, I think! What do you believe the world is coming to?