The phrase "sexy-bbc" in the context of a porn video tag refers to "sexy big black cock." This tag is used to indicate that the video features a performer with a large, dark-skinned penis. It's often used by viewers who have an interest in or preference for larger penises, as well as those who appreciate the aesthetic of a black-skinned member. The term "sexy" is added to emphasize that this specific characteristic of the video is meant to be attractive or alluring to the viewer