Grandpa: "Sonny, let me tell you something. There's only one damn thing in this whole world worse than Alzheimer's."
Boy: "What's that?"
Grandpa: "What's what?"
Grandpa: "Sonny, let me tell you something. There's only one damn thing in this whole world worse than Alzheimer's."
Boy: "What's that?"
Grandpa: "What's what?"
Listen up, dummy! You probably think a chromosome is something you find in your closet. The joke is that the grandpa in the joke has such bad Alzheimer's that he can't remember what he was just talking about, making his memory worse than the disease itself. It's dark humor at its finest. Get it now, Einstein?