The phrase “bug off,” to my ears, is a dated colloquialism, a mild expletive, synonymous with “leave me alone” or “go away” in the sense of a pesky kid underfoot keeping me from reading the newspaper. I would probably use “buzz off” before “bug off,” but I hear “buzz” as a variant of “bug” in that context.
The word “bug” in this sense is derived from the British English “bugger“, meaning sodomy, but used more often in the UK as a general purpose expletive. So “bug off” at one point meant something like “fuck off” but at least in American English has become progressively milder over time.
It came into English either via French, where “bougre” or “boulgre” meant “heretic” or via German “buger” for “peasant, blockhead.” Spanish “bujarrón” and Italian “buggero”, both with the sense of “sodomite”, and the Venetian “buzerar”, “to perform sodomy”, are derived from the French.
In all instances, the word was ultimately derived from the ethnonym “Bulgarian” (Latin “bulgarus”), which is where it starts to get interesting.
In medieval France “Bulgarian” was a synonym for “heretic” because of the supposed connections between the Cathars — sometimes referred to as the Albigensian heresy — of southern France and the Bulgarian Bogomil movement.
Reconstructing the history of a suppressed religion is always hard, because we rely on the evidence of the victors, and the history of the Cathars is shot through with lots of romantic claptrap. For example, the Nazis went looking for the Holy Grail (really!) in a former Cathar stronghold in southern France during WWII.
The religion of the Cathars, which was brutally suppressed in the 12th century by the Albigensian Crusade, was strongly dualist and gnostic. It’s a fun game to try and figure out why that religion flourished in that place and time, and did it have connections to Manicheaism, a similarly gnostic and dualist religion which also died a heretic’s death? There are superficial similarities, especially the central role of renunciant ‘clergy’ — the Cathars rejected the Catholic priesthood but retained the idea of apostolic succession and some sacerdotal role for the elect — in both religions. The link would be the Bogomils, a less well known movement with similar outlines but with stronger ties to older gnostic traditions, at least to the Armenian Paulicians.
There is evidence of contact between Cathars and Bogomils, and the interesting word history of “bugger” and “Bulgarian” is suggestive in this regard — European languages widely considered “Bulgarian” to be a pejorative synonym for “heretic,” and thus the all-purpose sodomy slur, which is standard insult material from high school locker rooms to medieval inquisitions.
Indeed, the best evidence we have for the religion of the Cathars comes from the detailed records that the Inquisition kept on their investigations and trials of the heretics. In fact, the institution of the Inquisition was created to combat the Cathar threat, and only later extended to persecute others.
One of my favorite ‘local history’ books is Emmanuel Le Roy Ladurie’s classic Montaillou: The Promised Land of Error, which is based on the meticulous records that the Inquisitors kept on their Cathar victims.