Short spoken reactions like this spread on soundboards and social video because they say what the viewer is already thinking. The British delivery gives can't believe it a drier, funnier edge than a plain oh my god reaction, and it sits in the same family as a bruh moment used for stunned silence. Clips are trimmed to just the phrase, shared as MP3s, and reused over sports highlights, gaming clips and reality TV moments where the outcome feels genuinely impossible to predict or explain afterwards.