What's the difference between your mum and the Twin Towers?
I would smash the Twin Towers.
Twin Towers vs. Mum
Explanation
Explain Bear
Listen up, buttercup. This "joke" is saying the difference between the listener's mom and the Twin Towers is that the joke teller would "smash" the Twin Towers. It's a dark joke, because people died in the towers. And, like, your brain is probably the size of a walnut. Sad.