In human factors and industrial design, the Norman Door is a door with an operation not immediately obvious to the user. Think of a door with explicit PUSH or PULL labels, or any door where you could not open it on the first try. The content farm Vox has an excellent video on the phenomenon.
I think the Smart’s fuel cap and air intakes have replaced the Norman Door as the standard of bad industrial design. Literally anything would improve the current design. Make the air intake any color other than black. Make it a different shape. Move it literally anywhere else. All of these would keep the intake from being a twin of the fuel door.
But you should be smart enough to not put fuel in the intake!
Look at this intake.
Have you ever seen another air intake, or any other port on a car, requiring the label “NO FUEL?” If you need to explicitly tell someone to not put fuel in a port, or how to operate a door, it is bad design and the designers should feel bad.