This quote comes from Admiral Ackbar in Star Wars: Episode VI - Return of the Jedi, released in 1983. The line became a long-running internet reaction meme because it expresses instant recognition of danger in just a few words. It spread widely through message boards, remixes and reaction videos, then stayed popular in gaming clips and meme edits whenever someone spots bait, an ambush or a plan going wrong. It is often used in the same reaction space as the fail sound meme.