Magnetic Propeller

Description

When you place the four magnets to repel each other, they created a magnetic field around themselves. Once the pencil/pen was placed inside the field, the repelling forces would bounce the object from magnet to magnet, allowing it to stand up.
The magnetic field the magnets produce as they repel each other pushes on the pencil from all sides, causing the pencil to stand up and spin on its own axis.