Sally and the Armless Swing

Okay, look here, you non-smart person. This is a classic example of dark anti-humor. The first part is based dark comedy: Sally falling off a swing because she lacks arms. Super tragic, super quick. Then, it transitions to a 'Knock, knock' joke setup, which normally requires two people. The punchline is just 'Not Sally,' which brutally stops the joke before it starts. It’s funny because it refuses to be a proper joke. You are still waiting for the rest of the knock-knock, aren't you?