Honestly, I think they writers assumed Sarah was there with Bristol, who unfortunately has had too much sexual publicity already.
When I heard Sarah was there with her daughter, I thought Bristol, myself.
That said, just because someone is considered an adult child of a celebrity does not mean crass things should be said concerning them.
Let's just pretend, for a moment, that was true (which we know is not. It was news the moment it happened) . His crass joke would be okay then?
He apologized with an another insult!
Look, I know it's good to be gracious and bad to take up offense but Letterman an insincere SOB and that is all there is to it. I can't forgive him because he did not offend me. But I will not forget this and nobody else should either. He is what he is and people will be reminded of his nastiness every time I hear his name. He has done permanent damage to his reputation.