I encounter to a dialog between two people while struggling on Cutting in line situation.

and here is the dialogues:

A: Hey man, the end of the line is over there.   
B: Yeah...  
A: No seriously, I was here first, and you can’t cut in
the line like this.    
B: Says who?  
A: I do!  
B: **So sue me!**  
A: Alright...that’s it....   

**(and here they start to punching each other!!!)**

When I see my dictionary it says that the meaning of `sue` is to make a legal claim against someone because they have harmed you in some way.

But I'm pretty sure that the **Sue me** expression has a different meaning in this context.

please help me out!