It happens:

Vice President Nelson Rockefeller appeals to the younger voters at this 1976 rally for Bob Dole (in bkgd.)

When George Bush was Governor of Texas he gave the camera a "One-Fingered Salute" before going on the air. While Bush may not have been the Commander-in-Chief at the time, this video is historically significant because the highest ranking U.S. official caught flipping someone off previously was Vice-President Nelson Rockefeller. Mr. Rockefeller was thought to be in the first stages of dementia at the time and died two years later. The same thing could be argued about Bush, but two years later he was made President.
And of course, the bird is flipped in every picture ever taken of any group of guys in the military...except maybe the Air Force...
heh heh heh
I don’t know whether VP Rockefeller “was in the throes of dementia,” I doubt it, because he was having a second helping of Megan Marshak, a 27-year-old research assistant. One version said Rocky had a massive heart attack and she was pinned under him. The way I heard it, she was astride him and attired in cowgirl boots and hat.
This being the mid-1970s, she didn’t need implants and he didn’t need Viagra.