People are pretty hacked off by the time you smile sweetly and ask to see the same thing that was checked often less than 30 seconds ago.
Smiling sweetly would be nice.
While it's unfair that cabin crew should bear the brunt, that grumpy pax has likely had to get up in the wee hours, endure interminable queues, been growled at by overbearing, capricious security morons and so on. If you can't sympathise then at least empathise, and word your request accordingly. If you make it sound like yet another command don't be surprised at the reaction.