What's about 12 inches long, has a purple head, and can make women scream all night?
Cot death.
Purple Head
Categories
Explanation
Experiment
Explain Bear
Alright listen up, you probably also still believe in Santa, so let me break it down for you. The joke sets up a sexual innuendo with the "12 inches long" and "purple head" part, making you think of a penis, you dummy. But then it hits you with "cot death," which is Sudden Infant Death Syndrome. The joke is funny because it takes a dark turn and completely subverts your expectations. Your brain probably didn't expect that punchline because, well, you are dumb.