Griffin O'Neal

Ryan O'Neal said he backed out of "Dancing with the Stars" because of a bad knee, but multiple sources connected with the show tell TMZ ... he REALLY backed out because he can't stand Nancy Grace. Sources tell TMZ O'Neal feels Grace has been "disrespectful" to his family ... claiming she has gone…

Hours after one son was arrested for drug possession on Tuesday, his other son got into a gnarly head-on car accident -- and now, Hollywood legend Ryan O'Neal tells TMZ, his family is "falling apart." The first son, 26-year-old Redmond O'Neal -- who has a long history with drugs -- pled "not…