Possibly an abbreviation of the BeeGees, a popular 70's group of 3 brothers. In fact, the BeeGees come from B.G. - Brothers Gibb. Well known for 'Stayn' Alive,' also 'Jive Talkin'' and 'How Deep is Your Love?' Integral in the phenomenally popular soundtrack from "Saturday Night Fever."
Saturday Night Fever is in fact the most popular movie soundtrack in history, featuring many tracks by the BG's.
From the French abbreviation "Beau Goss" meaning beautiful, handsome man. This abbreviation is often used to refer to a boss playa. He is man that owns respect from from all fellow BGs. His other bros wanna be a BG like him and try very hard to achieve this legendary alpha-male status.
Peter is such a douche, he hooked up with rebecca and now he's ignoring her." "No no no my friend, that is not a douche, THAT is a BG.