Hao de is a common Mandarin expression for okay, got it, or alright, and as a sound it circulates mainly as a tiny reaction clip rather than as a line tied to one famous scene. Its appeal is practical: the phrase is widely understood in Mandarin-speaking communities, it is polite without sounding formal, and its half-second length fits captions, replies and rapid-fire edits. Because of that, creators often use it as a neutral, low-drama yes that adds a touch of language and personality without interrupting the pace of a video.