Last time, I couldn't tell what the guy behind the glass screen was actually asking me to do, which irritated him immensely. "Lef'and." "Lef'and." "LEF'AND." It took a few tries for me to realise that what he was trying to say was "Can you put your left hand on the scanner, please?"
Maybe it's because I'm British, but I find the British border and security people far more pleasant, which is strange because on the whole, I find British people colder than Americans. Even when something goes wrong, they're apologetic (I was randomly picked for a full pat-down last time I flew out of Manchester, and it was all done with friendliness, good humour, and apologies for delaying me slightly.)
"Please" and "thank you" cost nothing, and would likely be quicker than these repeated barked orders. I like the American people--on the whole, I find them pleasant, polite, good-humoured, decent people. I mean, I am marrying one! So where do they find these people who work on the borders? Every single time I go through, I'm incredibly nervous of doing something slightly wrong, which makes me more nervous because I look nervous and worry they'll think I'm up to something. It's terrifying.