The Cathars were one of the more interesting Christian heresies of the Middle Ages (12th Century - originating in southern France). They had heavy Manichean influences ("This world is evil, and the Lord of this world is the Devil"). They thought the God worshipped by the Catholic church was Satan. The term "Cathar" comes from "catharsis." They believed that one became moe perfect by suffering in this world, and accepting it.
They were non-violent, non-hierarchal, disengaged from political processes, didn't pay Peter's Pence, etc. and so were prime candidates for burning by the Evil Empire (oops, the Roman Catholic Church). The leaders, or Perfects, were so non-violent as to become vegetarians, did not engage in any form of sexual relations, and gave up all worldly goods - they really made the prelates of the Catholic Church look bad.. After their destruction, some of their ideas lived on, eventually emerging in the Protestant movement in different form.
A form of Catharism took root in Bulgaria. As a slander, they were accused of homosexuality...and eventually Bulgars became buggers. And so the one of the less-than-polite references to male homosexual acts - buggery - came from slanderous religio-political propaganda against a Xian heresy whose members (ideally) did not have sex.