It's like how apparently "shag" is the equivalent of "fuck" in the UK, but in the US it typically refers to a type of carpet.
In fact, I only heard it [i.e., "bugger" ] in Monty Python and thought it was just another funny English word like "codswallop" or "git" or "odds bodkins" (the last of which was so bizarrely English that I didn't even attempt to understand what it was supposed to mean). It wasn't until I got to law school that the word came up during a Constitutional Law discussion of sodomy laws (which at the time were still legal - this was 1997 and I was 22).
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*