Hi Tracy, OG (Original Gangster)  is a slang term for someone who's incredibly exceptional, authentic, or "old-school" and it's not offensive.

Original Gangster: It’s a term used by younger guys to show respect and to acknowledge the guys that came before them. He’s an OG => I respect him. He’s one of the first (original) people doing whatever it is. It was first used for people living the street life selling drugs or in gangs, but now it can be used for any profession or anything to denote seniority in a person.