Abreviation, to be well hung, have an abnormally large penis, it is usually split into three parts, Senior, Intermediate and Junior starting at the tip going to the base, Junior and Senior interchange but Intermediate is always in the middle. If you are FBS you bang a lot of birds, but don't like bragging about it.
Geoff likes boys and willies
Jones: FBS! dude, i got that Fat Boy Swag
Jones: dude help me out of this jacket im stuck (starts to sweat and is struggling to breathe)
Glenn: haha "FBS" (Fat Boy Struggle)
Jones: Thanks man! (sarcasm)