The sound comes from the Among Us meme culture that exploded in 2020, when the social deduction game became a streaming phenomenon. In the game, crewmates try to identify the impostor, and sus, short for suspicious, became the universal accusation. RedIsSus in the original description points to the common joke that the red player is always guilty. Clips and edits using the phrase spread across TikTok, YouTube and Discord, turning a simple game callout into shorthand for calling out anyone acting shady, guilty or obviously fake in everyday online humor.