usually denoting some one as crazy. In later years to describe some one who usually believes everything is a conspiracy or illusion. Brought on by a belief that there is a invisible, intangible, army of Liberal Jew Communist, trying to control their mind with RF signals. So as a means of "defense" against the unreal onslaught against the LJCPMCM (Liberal Jew Communist Propaganda Mind Control Machine or media) they start covering their head with Tin Foil. Made famous by Mel Gibson, though mostly worn by the staff of the Fox News network.
Guy One: OMG, that guy must be out of his mind!
Guy two: Yeah, that is Bill O'Reilly for you, he is a total TIN FOIL HAT WEARER.