Bruh started as African American slang for brother before becoming a short Vine-era reaction in the mid 2010s, when a clip of a young man saying it in disbelief spread widely. The cleaner sound effect version was reposted across YouTube and soundboards, then found a second life on TikTok and in gaming edits. Its flat delivery made it easy to drop over almost any fail without explaining the joke. Years later it remains a default shorthand for disbelief because one syllable does the work of a whole reaction face.