Sometimes stylized as "run up, get
done up". It is a warning given out to those that seem to be contemplating making a violent move against a person or group.
Run up, in this situation, is referring to someone "
running up" on another person with the intention of fighting or jumping said person.
In the given context,
Done up refers to someone being on the receiving end of a beating.
To put it simply, it means "You can run up on me and try to attack me if you would like, but if you do I'm going to kick your ass."