Someone on the extreme edge of whatever their -ism happens to be.

(coined by Perry de Havilland)

"Definition of a 'barking moonbat': someone who sacrifices sanity for the sake of consistency"
-Adriana Cronin

Although the term (often rendered simply as 'Moonbat') is very popular with conservative and libertarian bloggers who appropriately use it to describe the Chomskyite Left, it was always intended as a much more ecumenical epithet and has been correctly used to describe certain paleo-conservative and paleo-libertarians views. (also see idiotarian).

Contrary to some speculation and entries on Wikipedia, Perry de Havilland has stated it was was not originally a play on the last name of George Monbiot, a columnist for The Guardian, as he was using the term long before he met or had even heard of Mr. Monbiot.
Lew Rockwell is a libertarian barking moonbat.
by Shinryuu July 5, 2008
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a person who is acting in a silly or weird manner; interchangeable with silly goose
Look over there she is being such a moonbat.
by aslutforharry January 17, 2021
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A conspiracy theorist or pseudoscience peddler, and, in British usage, someone who is also on the far left.

Originally it was a political epithet used against the radical left by conservative politicians in the UK. It comes from a corruption of George Monbiot's last name, a radical British political figure. As it crossed the Atlantic, it became less political and more tied to remnants of the hippie counterculture, particularly the new age movement. So if someone says moonbat in the Queen's English they're likely a Tory, regardless of age. If they're American or Canadian, they're either a skeptic of any political affiliation or an aging conservative.
BrE: "Pay no attention to the failures of austerity; Grenfell was the fault of Labour moonbats!"
AmE: "If you believe that the government is trying to control the weather with chemtrails, you're clearly a moonbat."
by tomazgeofferzon February 15, 2018
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