Last time I visited San Francisco I had border officials twice just suddenly snap at me. While getting my luggage an official just randomly approached me an asked me some random question in an angry tone. Then when in line holding a piece of paper on which I had written my ESTA number, an official came to me and just pulled the paper from my hand, demanding "what's this!?". Additionally they flipped through my entire itinerary.

Consider that this is someone's first experience on US soil and it sets the tone for the whole trip. Nothing like this has happened in any of the other countries I've been to, including India, Vietnam, Cambodia etc.