Pentagon's Sides

Alright listen up, buttercup. This joke is dark. Like, really dark. It's playing on the 9/11 terrorist attacks, you know, when planes crashed into the World Trade Center (aka the Twin Towers) and the Pentagon? The joke is saying the Pentagon only has 4 sides when a plane hits it. That's messed up, man. And it's messed up that you don't get it.