I don't cross into the US often. Maybe 5 or 6 times in the past 10 years,
My best crossing was years back. It was a hot, hot day. Lines moderately long. I had a Bob Marley CD on, prolly too loud while waiting in line with the generator running, AC on the roof of the Roadtrek and dash both blowing cold. Guy in the booth, a burly, short black man with a gleaming shaved head, glared out at me as I reduced the volume, leaned out of the booth a bit with a snarl on his face and said "I'm really pissed at you". A bit shocked I replied., "Why". He said cause you are sitting in the air conditioning listening to Reggae and I'm here in this hot booth" And broke into a broad smile with a laugh.
On another occasion I was crossing in a Roadtrek van motorhome. I usually stopped at the last Pemex to pee in case of along line to cross and got into the habit of buying one of those microwave precooked hamburgers. I was munching as I pulled up to the inspection booth and was greeted by a skinny guy with a hawk face, looking strained, eyes darting around. He sort of mad dogged me I thought, but I kept munching. He paused, staring at me long enough to feel uncomfortable, then stepped out of the booth and slapped a yellow post it form on the windshield and told me to go to secondary inspection. I had no schedule to keep but thought it would take a while for inspection, what with all the storage spaces in the motorhome. I grabbed a book to read and went into the waiting area. After only a few minutes I was called outsides and told I could leave. As I pulled away I noticed the yellow form still on the windshield, stopped and removed it. It was a referral form to inform the inspector of the reason for secondary inspection. Scrawled at the bottom of the notes was "Kept eating his hamburger" and nothing else !! The fact that no one had read or removed the note and that I was not really inspected carefully led me to believe that inspector was not well thought of by his cohorts. So it takes all kinds.