Smh began as text slang for shaking my head in early internet forums and texting, then moved into spoken form as reaction culture grew on social media and video platforms. The short audio version became popular because it translates a typed expression into a vocal cue that editors can drop into compilations, streams and memes. It is now used less as literal speech and more as a universal signal of disbelief, which keeps it relevant across different communities and formats without needing a specific source show or character.