Crowd booing is one of the oldest and most recognisable audience reactions, heard at sports matches, talent shows and theatre performances whenever the crowd disagrees with what it has just seen. As a standalone sound effect it has become a staple of online reaction videos, memes and gaming streams, where a single burst can signal failure, disappointment or playful mockery without any explanation. Its power comes from familiarity: almost everyone recognises the sound instantly, so creators keep using it to puncture hype, roast a bad play and turn an awkward moment into a joke.