I am not sure it isn't just wishful thinking but that young man looks like a cat ready to pounce on a mouse????
Look at his left hand and the expression on his seatmates face...In a 'happy' situation like that one would think while it is proper for the Marine being addressed to be standing, the one sitting would at least look like someone is enjoying the moment.
The Sergeant is standing at attention, while jfk points to his ribbons. It is appropriate for the Sgt. to be at attention while being addressed by a US Senator, even if he disagree with him.
The sitting Marine really tells the story. IF GWB had entered, ALL the Marines would have to come to attention, as GWB is the CIC. But after that there would be group photos, with GWB having his arms around the Marines. A very popular saying is, "if you talk the talk you better walk the walk" (i.e., actions speak louder than words)...and GWB "walks the walk" when dealing with the military. All the time, and it is sincere not contrived or photo ops only. Military guys can spot a phony a mile away, and usually express it in their actions, but not in a way to get themselves in trouble. (Witness the Sgt. at attention, the other Marine sitting.)
Semper Fi! USMC 1970-1981