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.