The clip comes from The Simpsons, the long-running animated series centred on the Simpson family in Springfield, with Homer as the father known for blunt, lazy reactions. C'est nul is taken from the French version, which is why the line is in French rather than English. Online it sits alongside other Simpsons reaction sounds like Nelson's HA-HA, shared by French-speaking fans and editors who need a quick dismissal. It stays popular because Homer's voice is recognisable even to viewers who do not speak French, and the meaning is clear from his tone.
About this sound
Homer Simpson says c'est nul, French for that's terrible, in this short Simpsons clip used to react to bad ideas, fails and disappointing results.
Homer Simpson delivers the line c'est nul with flat disappointment, the French phrase meaning that's rubbish or that's useless. The delivery is short, dry and instantly dismissive, with Homer's familiar voice making even a simple put-down sound funny. It lands like a one-word review for something that has completely missed the mark. Creators use it when a plan falls apart, a joke fails to land, or a result is so weak it does not deserve a longer explanation. The brevity is the joke, cutting a scene off before anyone can defend it.