I have met only a single non-friendly black lab (and considered her a result of inbreeding with a non-conforming body type and violent temperment; she was put down after attacking and blinding a cat and nearly-blinding a puppy.)... all others have been examples of an eager-to-please personality, playful temperament, and complete devotion to the game of fetch.
One of my favorite examples of this breed is one by the name of Bucky.
His passion was camping, marking as many trees as he could in the forest, and bringing people sticks to throw for him. When my wee'en decided to hike down the mountain (got about 100 yards down the road before turning around...) Bucky was the escort, walking with her. Sadly, he passed away three years ago. Always missed and never forgotten, his love for those he considered his people goes on in the spirit of damn near every labrador retriever.