It's really no surprise that Harry is so dumb that he thought this would fly. What surprises me is the Royal chain of command this decision to dress as a Nazi must have gone through. Harry being somebody who has never had to buy anything or shop in his entire life, so presumably Harry states "bring me a Nazi uniform," and a line of Royal advisers and servants set about this not ever questioning the implication.
I just wonder how many Tsunami care packages Harry will have to pack to make ammends.