When does a Pentagon have 4 sides? When it's intercepted by a plane.
Pentagon's Sides
Explanation
Explain Bear
Alright, listen up, buttercup. So, usually, a Pentagon has five sides, right? But in this joke, the Pentagon gets "intercepted by a plane," which is a dark reference to the 9/11 attacks. The joke implies the Pentagon only has four sides because one side was destroyed when the plane hit it. You probably think the earth is flat.