The New Penguin Dictionary, 2000:
bugger (..) Word history
Old French bougre heretic, sodomite, from late Latin Bulgarus Bulgarian. Bulgarians belonging to the Orthodox Church were regarded as heretics by the Catholic Church; heretics were traditionally suspected of forbidden sexual practices.

Bulgāriem veicas līdzīgi kā čukčām, arī to tautība ir kļuvusi par lamuvārdu.

Un jā, "bulgārs = ķeceris = homoseksuālis" pats par sevi arī ir interesants secinājums.