I just experienced positive, polite, friendly, and efficient security screening...
... not in the US, of course, but in Japan.
Seriously, went through security four times (2x in Sapporo, 1x each in Tokyo Narita and Haneda), and found not only were they thorough, they were polite, courteous, and soft-spoken, and had a smile on their faces at all times.
Yes, I had to show my boarding pass, take my laptop out, and they found a mini shampoo bottle that I had forgotten was in my bag, but did so without any fuss or drama, and without once having to raise their voices or bark orders to the passengers.
Japan is truly an amazing country! And is proof you can have good airport security without the circus and the shouting we have to put up with in most airports in the US! (And Japan is no stranger to terrorism either).