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"
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.