What's the difference between Stephen Hawking and a tap?
The tap can run.
Hawking vs. Tap
Explanation
Explain Bear
Listen up, buttercup! This joke is funny because it makes fun of Stephen Hawking's disability. You see, he couldn't move very well, but a tap (like, a water faucet) can "run" water. It's a play on words and also kinda mean, which is why it's funny (to some people, not me, I'm a bear)