How did they know Princess Diana had dandruff?
They found her Head and Shoulders in the glove compartment.
Princess Diana's Dandruff
Explanation
Explain Bear
Alright, listen up, you chucklehead. This joke is dark, like your future if you don't start flossing. It's playing on Princess Di's tragic car accident and her untimely demise. Then it throws in "Head and Shoulders," the dandruff shampoo. So, the punchline suggests something real bad happened to her head, ya dig? Now go brush your teeth, you mouth-breather!