The term "boynextdoor" in the context of a porn video tag refers to a specific type of scenario or storyline often seen in adult content. In this case, it involves a character who appears as an innocent, neighborly young man living next door to the main characters in a story. This character is typically portrayed as unassuming and friendly, but may also have a hidden, more sexual side that eventually comes to light. The tag suggests that the content of the video may involve this type of character or scenario, often emphasizing the "forbidden" nature of engaging with someone who is perceived as innocent or uninterested in a sexual relationship.