What if the slums of Ankh-Morpork had their own mafia?

A mafia with their own way of doing things, maybe not as cunning as Havelock Vetinari, but smart in their own ways. These are very poor, under-resourced people who aren't quite organized enough to disappear into the crowd, and they get caught by the City Watch on a regular basis, but they find ways to exploit the system. They're not quite cunning enough to get away with things, but they always manage to avoid getting punished. They have their own way of doing things, their own traditions and rules, that are very different from those of the City Watch or the Patrician.