Just have to live with them. Go up to them and ask them to move..They want then lay on the horn. Civility first I guess.
We emptied our tanks, several years ago. No one around. Everybody uses the one at service center. Had barely connected the sewer hose and some yoyo caam up and parked on bumper and hit his horn. I took the five minutes or so required and he honked a couple of times.
I didn't say a word. We pulled over in the huge empty lot and fixed dinner. He was at the station fifteen or twenty minutes.
It usually takes us ten minutes or so to flush tanks but we hurried to accommodate bozo.
Just the way some people are.
Try to avoid them and not let them bother you.