I was on the other side of this perspective a couple of weeks ago. I had finished fueling my coach but needed to fill my DEF tank. Unfortunately, my DEF tank is on the wrong side of the coach and I had to use a 5 gallon container to fill it.
The truck behind me was furious that I didn't pull ahead after fueling. He was screaming at me. I had to finally walk up to him and explain that I wasn't done with the pump yet and would move forward as soon as I finished pumping my second load of DEF into the container.
Once I explained what was happening, he calmed down. He simply didn't understand my predicament and that I was doing all I could to move along.