bugger: [16] The Bulgarians, belonging from the early Christian era to the Eastern Orthodox Church, were regarded by Western Europeans as heretics. Thus it was that the Latin word Bulgarus came to be applied generically to any heretic, and eventually specifically to the Albigenses, a Catharistic sect in southern France in the 11th to 13th centuries. It passed via Old French bougre and Middle Dutch bugger into English, acquiring along the way bigoted associations of heresy with anal intercourse. The weakened use of the word as a general term of abuse dates from the early 18th century.
bugger (n.)
"sodomite," 1550s, earlier "heretic" (mid-14c.), from Medieval Latin Bulgarus "a Bulgarian" (see Bulgaria), so called from bigoted notions of the sex lives of Eastern Orthodox Christians or of the sect of heretics that was prominent there 11c. Compare Old French bougre "Bulgarian," also "heretic; sodomite." Softened secondary sense of "fellow, chap," is in British English from mid-19c. Related: Buggerly.
bugger (v.)
to commit buggery," 1590s, from bugger (n.). Meaning "ruin, spoil" is from 1923. Related: Buggered; buggering.