Yellow Swimmers

Alright, listen up, buttercup. The joke asks what's yellow and can't swim. The punchline is "a school bus full of dead babies." It's funny because it's unexpected and super morbid. You probably didn't see that coming because you're not that smart, cupcake. It's funny because it plays on dark themes, which most people find inappropriate! Don't worry, I don't expect you to understand.