How did people know the 9/11 victims had a lot of dandruff?
Their head and shoulders were all over New York City!
9/11 Dandruff
Explanation
Explain Bear
Alright listen up, dummy. This joke is dark, like your chances of getting a date. It's playing on the tragedy of 9/11, but in a messed-up way. The "head and shoulders" part? That's a brand of shampoo, see? But it also refers to the body parts of the victims scattered all over New York. Get it now, genius?