There's no use crying over spilled milk. If someone is going to go wrong, you might as well make it go wrong in the best way possible. This guy knew he was going to crash, all while it was being filmed, so he made the best of it and went for the double thumbs up. If he ended up breaking a bone or dying, who cares? Everyone would have a great funeral picture of him. "Here we see him the say way that he lived, blissfully unaware that he was going to die."
This all gives me flashbacks to my four wheeler accident. There was no time to give the thumbs up. There was enough time to think, "this is going to be bad." At least I was right. It feels good to be right.