"Nobody likes him, nobody wants to work with him", she said.
"If it were a one-off, you might say, 'OK, fine.' But he said I was unqualified", she recalled.
Hostin later described Sanders as a "get off my lawn kind of guy" who admitted to disliking pleasantries such as wishing others a happy birthday.
"It's all just baloney and I feel so bad that people got sucked into it", she adds.
Hillary Clinton caused a firestorm when comments she made about former rival Sen. "We're still in a very vigorous primary season", she noted, vaguely alluding to the tense political climate and even more strenuous Democratic race.
In the documentary, Clinton says of Sanders: "Honestly, Bernie just drove me insane".
Sanders has denied making the comment but Warren confronted him about it at the Democratic debate in Iowa last week, saying: "I think you called me a liar on national TV". Rose followed up by asking if Clinton will endorse Sanders if he wins the nomination, and she demurred.
Just a couple of days into opening arguments, the Senate's impeachment trial is already impacting the presidential campaign trail, as shown by CNN's announcement that it would cancel town hall events for Democratic presidential candidates because of it. In an interview with the Guardian this month, the Republican consultant turned Trump critic Rick Wilson said Clinton "beat [Bernie] fair and square, he took his ball and went home".
Nick Merrill, Clinton's spokesman, tweeted that 'we all need to work our heart out for the nominee, whoever that is, and @HillaryClinton, as usual, won't be any exception'. "He hurt me. There's no doubt about it".
Clinton, in the interview, also refused to say if she would back Sanders - whom she faced off against in the 2016 Democratic presidential primary - in 2020.
Sanders played down the attack in the documentary, telling reporters that he was focused on Trump's impeachment trial, which kicked off in earnest Tuesday. He refused to comment on Clinton's critical comments, saying only in a statement, " Together, we are going to go forward and defeat the most risky president in American history".