"Paper is 2D!" said Pen.
"No, it's 3D!" said Pencil.
After Pencil proved it to Pen, Pen said, "Oh, I suppose you're write."
Listen up, buttercup. This joke is all about words sounding alike. The pencil showed the pen that paper is actually three-dimensional (3D), not just two-dimensional (2D). Then the pen says, "I guess you are write." Get it? Write sounds like right!