Last week I got tossed onto a plane and flown to Mexico on very short notice (5 hours). First time ever going outside the US. My passport photo was over a year and a half old, and back when I weighed 260+ lbs. It was a fun experience. Landed in some big retirement town right in the middle of Guanajuato, Mexico up in the mountains. Beautiful houses all over, lots of rich retired people.
Didn't have any issues until I had to come back to the US and sat in line, 5 places from the front of the line, at Customs for an hour and a half. Then the guy didn't believe it was me in my passport so I had to give him my drivers license too. Made it to my connecting flight 10 minutes before takeoff.
They directed me to the "US Citizens" line, but about half the people in the line were visitors who needed to be fingerprinted/photographed. This was in Houston, coworkers landed in Dallas and said their lines were better segregated and they got through Customs in no time.
Customs was much easier in Mexico "Hola, were are you staying?" "Ok, press this button" "Ok, have a good time."