At the checkpoint the officers looked at me with disinterest (probably a combination of the dull routine and because I looked like a white US citizen). First they asked me if I was a US citizen and I said no, and suddenly they were looked far more interested. They asked to see my passport and informed me they'd need to search my vehicle and I was to open the trunk. I complied, opening the trunk and passing my passport to one officer while the other went to the rear of the vehicle to start a search. A few seconds later the officer with my passport notices something and urgently signals the other officer. At this point I was worried that my paperwork must not be in order and that I was in trouble. Once the other officer rejoins the first they briefly confer and then they hand me back my passport and apologize profusely for the inconvenience saying that they didn't realize that I was a diplomat before sending me on my way.
The kicker is that I wasn't a diplomat, merely a bureaucrat on an official trip to the US and any "diplomatic immunity" I had was the thinnest kind of intergovernmental courtesy.
At first this story was funny to me as the time I accidentally wielded diplomatic immunity. However, more recently I find it less amusing as instead I consider it a tale about how the changing assumptions of the officers significantly affected the nature of the interaction and how different the interaction could have been if their assumptions had been less favorable.