Sorted list of (username, napp_name) of disabled napps.

        The difference of installed and enabled.

def get_disabled(self):
        """Sorted list of (username, napp_name) of disabled napps.

        The difference of installed and enabled.
        """
        installed = set(self.get_installed())
        enabled = set(self.get_enabled())
        return sorted(installed - enabled)