What is the rarest skin in FN?

Excuse me, could you please clarify what you mean by 'FN' and the context in which you're referring to the rarest skin? Are you referring to a specific game or platform? If so, could you provide more details? Additionally, could you elaborate on what makes a skin rare in the context you're discussing? Is it based on scarcity, exclusivity, or some other factor? I'm eager to understand your question better and provide an accurate answer.