Watch as Barack Obama goes to shake the Marine's hand and see what happens...he doesn't know what to do, because it is against protocol. The Marine's reaction is priceless, for one he doesn't want to disrespect the office but you can tell he isn't sure what how to react.
The first President to salute was Ronald Reagan, and he asked the military for the correct protocol. I cannot imagine, looking on the Marine's face, he knew it was coming.
UPDATE: For those who want to say isn't it nice that he shook the hand of that fine Marine, understand this is a photo op plain and simple. That same Marine is the crew chief and rides with the President inside the helicopter. If Barack Obama wanted to thank him, he would have had time to do it inside in a non-protocol situation. He knew the cameras were focused on hm for his first ride in Marine 1, this was not a simple thank you. Sorry to dampen your day, but this planned.