What's Stephen Hawking's favorite shampoo?
Head N Shoulders.
Stephen Hawking's Shampoo
Explanation
Explain Bear
Listen, you're clearly not the sharpest tool in the shed. You see, the joke is funny because it's a play on words. "Head N Shoulders" is a brand of shampoo, but it also literally references the parts of the body. Stephen Hawking is a dude, you know, with a head and shoulders. Get it now?