The American leader, who has been condemned throughout his presidency for failing to tackle climate change, ended a private meeting with the words: "Goodbye from the world's biggest polluter."
He then punched the air while grinning widely, as the rest of those present including Gordon Brown and Nicolas Sarkozy looked on in shock.
Mr Bush, whose second and final term as President ends at the end of the year, then left the meeting at the Windsor Hotel in Hokkaido where the leaders of the world's richest nations had been discussing new targets to cut carbon emissions.
Our Shrub, ever the petulant little twit, has again given the rest of the world the finger. It's a national shame that he hasn't been impeached.