Or you have driven at 200mp/h on the Autobarn in Germany.
Obviously perfectly legal in Germany, but seriously illegal in the USA, so the border guards will deny you entry for breaking a US law while you where in a country where it's not illegal! insanity!
Obviously perfectly legal in Germany, but seriously illegal in the USA, so the border guards will deny you entry for breaking a US law while you where in a country where it's not illegal! insanity!