He gets flashbacks, and they compel him to park in handicapped spaces, go to restaurants and forget to pay, and butt to the front of the line at movie theaters. The poor man has such bad PTSD that he forgets who he is. So he asks the maitre d’, the movie usher and police officers who object to his behavior, “do you know who I am?”
The paranoia even causes him to dock his sail boat out of state. But it's not the Viet Cong who haunt his nightmares it's the FBI.