on the lonely planet thorn tree forum there is an extensive thread about the same experience. this is all too common, I spent some time in Lima where this happens a whole lot more to foreigners than it does here in BA. search for the post on there, its interesting because it seems that 5 or 6 travelers described the same exact situation as yours, maybe with the same assholes? my advice? get equally aggressive and punch one in the face =0)