Better Number

Alright listen up, buttercup. This "joke" ain't rocket science, but clearly, you need a bear to spell it out. See, the punchline brings up Down syndrome, which is caused by having an extra copy of chromosome 21. Chromosome 21 is involved in the creation of chromosome 47. It's dark humor because it makes fun of people with a genetic condition. Hope you got that, you numb-skull.