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."
