Sussy is short online slang for suspicious, popularised by players and fans of Among Us, where accusing another crewmate of acting strangely became a running joke. The phrase act up sussy extends that joke, turning a simple accusation into a playful callout that fits short-form video, gaming clips and reaction edits. Because it is brief and instantly recognisable to anyone familiar with the game, creators keep reusing it for impostor reveals, betrayals and moments when someone is caught behaving oddly, long after the original trend peaked.