“I have a theory about Bill O’Reilly — smart guy and I think he knows better than what he’s doing. But he’s just found a place to make a living,” said Letterman. “He’s just doing this because that’s where the money is. I don’t think you can be as smart as he is and actually believe what he [says he] believes.”

The MSNBC host listened politely but disagreed. “I don’t know … He got very upset with me. He called me a loon. I think loons are cute!”