The first time my wife and I travelled on the Eurostar, years ago, a French official asked to see our passports as the train was speeding towards the tunnel. I handed him my recently renewed passport for inspection. He looked at it, looked at me, looked at it again and then loudly and theatrically said (to be read in a stereotypical French accent) "You must come wiz me.... TO PRISON!!". There was a long pause. I didn't know what to say. He then continued, in the same manner "You 'ave not....SIGNED YOUR PASSPORT!!". Then he laughed and handed me a pen. I laughed nervously, signed it and that was that. :-)