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Bush was amused by Colbert asking for the sexy female reporter to call him later, and he was amused by Colbert bumping into the wall when he tried to leave through the drapes behind the podium. He was also slightly amused with Helen Thomas revealed as the chauffeur in the last moment. Aside from all this, however, he looked like he knew he was the butt of the whole joke (which he was) and was not enjoying it at all. When some of folk walked by in front of the podium, he watched them leave with a "Wish I could follow them" expression, and at the end he was doing the fingers-of-one-hand-on-palm-of-the-other clapping that people do for ritual purpose when they didn't enjoy something but have to clap for politeness' sake.
I'll admit my own patience was wearing with the overlong "carkey fumble" schtick, though Colbert rewarded it properly by suddenly having him remember to just push the chirper to open the door, but Bush was certainly not enjoying himself at that point.
All that said, while Bush was doubtless pissed, part of why he was pissed was he was being skewered by someone who was actually funny, and even he cracked some smiles at Colbert's jokes.
I'd love to see a camera on Justice Scalia during the whole routine. From what I saw, Scalia was nearly laughing out of his chair the whole time, though this is likely because if there's any Republican who gets satire, it would be the notably snarkiest member of the Supremes.