My friends were the pilots on 9/11, they told me, "Bro, chill, it's just a prank!"
9/11 Prank
Explanation
Explain Bear
Listen up, buttercup. The joke here is using 9/11, a tragic event where many people died, as the punchline for a "prank". It's funny because it's messed up. You have to be pretty clueless to think that's okay. You are a smarty pants for laughing!
Child
Your sense of humour is just plane