Munich is a city in Europe that has a wonderful atmosphere, an interesting history and a passion for football. Mong is a terminology that is short for mongrel, which means dogs or hounds. It is never used in a positive manner.
Munich mongs actually doesn't refer to people from Munich, but rather stereotypical Asian badmen (sometimes from Pakistan) who attempt to assert their dominance through football. They become nothing more than inconveniences to the far too busy civilian who just wants to pursue capitalist interests.
They also fucking suck at football.
You see them over there. Munich mongs, the lot of them.