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O'Hare airport has one of the best passenger friendly security in my opinion. TSA officials are friendly. Once you show your ID and boarding pass before security, there is no further need to show either again except to have your boarding pass when you get on the plane. Some airports check both of these before security, then ask for them again when you pass the metal detector, even though you just showed them 20 feet away. Denver has one of the most rigid systems you can imagine and Las Vegas has one of the most inconvenient standing in line systems.
But you know what, I usually can avoid extra screening by smiling slightly and using the most relaxed posture possible. I just keep my month shut and keep myself amused by the stupidity in progress. And I take my time putting all my belongings and clothes back where they belong, regardless of what's going on.
Warning about Beijing. The screeners are young and inexperienced. They took my wet naps from my liquids bag. Why ? Because they contained some alcohol.