What does Stephen Hawking and a prostitute have in common?
They both charge.
Hawking and a Prostitute
Explanation
Explain Bear
Listen up, buttercup! This joke is funny 'cause it uses the word "charge" in two different ways. Stephen Hawking, the brainy dude, "charges" money for his smarts, like writing books. And a prostitute, well, they "charge" for their, uh, services. Get it now, genius?