The acronym for "gay
butt sex orgy". It is one of many terms used to describe sexual interactions, such as lso, "
lesbian sex orgy", mbso, "mixed butt sex orgy", and kgbso, "
russian butt sex orgy". There is a tumblr page dedicated to the subject: gbso.tumblr.com
Will: Hey Dave, want to have a gbso tonight?
Dave:
Man how 'bout an mbso?
Will: I
guess you're wanting some variety after only men for a few weeks.
Dave: Yeah, how about some Russians too?
Will: Ok I'll
ask Ivan to make the kgbso.