Sarah Silverman -- Joan Rivers 'Wasn't Done' Making People Laugh

Sarah Silverman took the passing of Joan Rivers very hard ... commiserating with Jimmy Kimmel Thursday night and cracking a few fashion jokes at Jimmy's expense ... like Joan would have.

Silverman told Kimmel she just heard from Joan last week -- she reached out to congratulate Sarah on her Emmy. Silverman added that Joan told the most "hardcore jokes on TV" on her show, "Fashion Police."