Head and Shoulders

Alright, listen up, nimrod. You see, Stephen Hawking, who was a genius scientist dude, had a disability that meant he couldn't move much. So, the "Head and Shoulders" shampoo thing? It's a play on words! It's funny because it sounds like "head and bolts". Because Stephen Hawking is in a wheel chair! Get it? The joke is about the head and... Ugh, never mind. Some people just aren't wired for comedy, and based on the fact that you didn't get the joke, I'm guessing you are one of them.