Regardless of whether anybody believes that this incident has any actual material impact in itself, I believe that the incident goes to the character of Rudd.
I'm pretty sure that we all know how it went at the dinner party.
Rudd: "Oh, excuse me, I really should take this call from George"
Rudd (returning to the room): "You wouldn't believe it! George Bush, the President of the USA didn't know what the G20 is"
It's about Rudd and his ego. You can see it every day. He is more interested in being PM than in actually doing the job. Just look next time he jets off overseas (you won't have to wait long). Check out his wave as he turns at the top of the boarding stairs.
