Green
FN stands for a far more explicit phrase, "green fuckin' nigga" that'
s used to refer to someone who is particularly suave or
cool. In its original use case, the term was fairly specific to the world of basketball. That'
s because the term originated from NBA 2K, a series of video games in which gamers get the chance to replicate an
NBA season and play with or against the stars of the modern
NBA.
In NBA 2K, a green shot is one where you nail the timing and release so that it has a high probability of going in. Green shots are considered the goal for many who play the game, a "Green FN" is a person who brings that kind of swagger to their life off the court, in addition to their game.
Essentially, then, Green FN is a term that started in the world of
gaming, and was eventually applied to real basketball and then to other circumstances
outside of basketball.