Princess Diana's Dandruff

Hey, listen up! So, the joke is that Princess Diana died in a car crash, which is already not funny. Then, the joke says she had dandruff and they found her "head and shoulders" in the backseat, which is a play on words since "Head & Shoulders" is a shampoo brand. Get it? The joke is really dark and not very funny because it's about a real tragedy and uses it for a dumb pun. You probably didn't get it because you think wearing socks with sandals is cool.