What you have described is the reason that conductors (such as metals) will act to reduce any polarisation within their structure. Polarisation is an imbalance of charge. In an object with a neutral charge overall, one region of the object may have a surplus of electrons, and thus have a net negative charge, and therefore another region will have a deficit of electrons, and thus have a net positive charge.
Now, what you say about metals is true, they conduct electricity and therefore current will flow in order to neutralise any imbalance in charge. However, this does not prevent them losing electrons by friction. The standard classroom experiment where you rub a balloon against your shirt in order to pull electrons from one to the other will still work with metals. Copper, for example, is often used as a conductor in wire form, but a copper rod may also be rubbed against another object to transfer electrons. This is called the Triboelectric Effect.
Also, although conductors when left on their own will act to spread charge out across their structure through current flow, it is still possible to polarise them (i.e. create imbalances of charge) using an external means. One such method is called Electrostatic Induction. In the picture below, moving a positively charged object near to the conductor in the electroscope pulls the electrons toward the top end, and as a result causes a local net negative charge here, and a local net positive charge at the bottom.
"Electroscope showing induction" by Sylvanus P. Thompson - Downloaded from Sylvanus P. Thompson (1881) Elementary Lessons in Electricity and Magnetism, MacMillan, New York, p.16, fig. 12. Licensed under Public domain via Wikimedia Commons.
Now imagine you were to suddenly cut the conducting material in the electroscope in half. The top half would be a completely independent object, and would have more negative charge than positive charge, a surplus of electrons. The bottom half would be similar, but would have more positive charge than negative charge, a deficit of electrons.
I hope this helps.