This sound is mainly shared online as a short reaction clip rather than a long quote with widely recognized context. In meme culture, ultra-short one-word sounds spread because they are easy to drop into edits, reposts and soundboards. “Fat” fits that pattern: it is quick, clear and useful for visual jokes about size, overindulgence or exaggerated reveals. Its staying power comes from timing more than source recognition, since creators can use it in many different formats without needing viewers to know any backstory.