Homework Assistance Offer Gone Wrong, Dude! 

Listen up, dummy! You really didn't get this? The teacher is making a morbid joke by comparing the explanation of homework to the destruction of the Twin Towers. The phrase "break it down" has a double meaning, referring to both simplifying information and the literal collapse of the buildings. This joke relies on the shock value and tragedy associated with the Twin Towers to create humor, highlighting your teacher's awful comparison to help you understand a difficult task.