Everyone knows that Bill O'Reilly and Keith Olbermann don't really like each other. In fact, the word "arch-nemesis" may be the most appropriate to use here. Now that Olbermann is officially out at MSNBC (and maybe running for Senate?), O'Reilly feels no closer to forgiveness. In fact, his heart is so full of ire that he apparently refuses to speak Olbermann's name.
In a segment on his show, he addressed the issue only by saying "a hateful commentator" at MSNBC was leaving — and when pressed by his guest, he still dodged actually vocalizing the word "Olbermann." Basically, O'Reilly has rendered Keith the Lord Voldemort of cable news.
This volley is an expected retort to the praise Keith Olbermann has been getting in the wake of his departure by other members of the media — including fierce defense and legacy-making by members of his old network, MSNBC.