'Boy Next Door' is closely associated with Gachi meme culture built around clips of Billy Herrington and other source material that spread through remix communities in the late 2000s and 2010s. The phrase became a recognizable in-joke across anime edits, mashups and forum-era meme videos. It stayed popular because the line is short, instantly identifiable to fans, and easy to drop into sudden-cut humor in the same way people use bruh or other quick reaction sounds.