moonbat

Etymology
From, first used in the 1940s by the science-fiction writer Robert Heinlein, then used in the term “barking moonbat” coined in 1999 by Perry de Havilland of “The Libertarian Samizdata”, a right-libertarian weblog. This originally referred to both left-wing and right-wing crazy people. Sometimes wrongly claimed to be a of Monbiot (from George Monbiot, British environmentalist and Guardian columnist).

Noun

 * 1)  A liberal someone with a left-wing ideology.