
Moonbat

"Moonbat" is a pejorative political epithet used in United States politics, referring to liberals, progressives, or leftists (especially the far-left), a possible parallel to the pejorative "Wingnut" attributed to American conservatives, and right-wing politics.
Etymology.
Descriptions of bat-like people on the Moon were part of the 1835 Great Moon hoax.
A long poem, "The Proving of Gennad: A Mythological Romance" by Landred Lewis (1890), uses the term "moonbat" to refer to unsound ideas, but not specifically political ones.
The term was used by science fiction author Robert A. Heinlein in the 1947 short story "Space Jockey" as the name of a rocket spacecraft used for the third step of a journey from the Earth to the Moon.