Can you charge a conductor (like a metal) rubbing?
While you can charge a dielectric (non conductive, like plastic) object rubbing, you cannot charge a conductor (like a metal) rubbing.
The reason is that in a metal the charges are free to move inside the material. If you add a charge in one zone of the conducting object, the other charges will automatically re-arrange to neutralize the charge.
In a dielectric the charges that you put on the surface of the object rubbing stay, there is no re-arrangment, because the charges of an insulator do not have the freedom to move inside the material.
So you can charge only some material rubbing.