Your rule of thumb is a good one, and one that I follow when I am coaching. On the other hand, yes, it is unethical for you to get an occasional call because of your reputation. All calls should be made based on the rules and the unbiased judgement of the umpire. Who is in the dugout should have no effect whatsoever.I have been around the softball world for 16 years, either as a coach, league board member, and ocassionally reluctant umpire. I have seen several umpires for over 12 years and they have seen me at the B/C travel level. Now several of them sometimes do my DD's high school games and I ocassionally see an umpire I know at a PGF tournament. Do I get the benefit of the doubt ocassionally on a close call because of my reputation, sometimes. Is it unethical-- no. Also many less experienced coaches don't know how to calmly interact with the umpires on various issues that come up during games.
My favorite rule of thumb I use is "If anyone but the umpire you are asking the question of can hear you, you are asking the question the wrong way"