Origin: This phrase/sentence was commonly used in the 1990s by students after the proliferation of legal litigation's in the media against large corporations.
The most notable examples that accelerated this phrase/sentence would be the people rising to sue large corporations such as McDonald's. People suing each other for little conflicts has also strengthened the use of the phrase.
However, in the 2000s, the RIAA's strike back, suing even children, has brought "so sue me" it a abrupt stop.
Person 2: So sue me.
Person 1: Aiyah, whatever.