Not surprised, but it is disheartening to hear regardless.
I've helped out and worked the bench, but am by no means "coaching" my son. So this is my take as a parent. A lot of parents these days are CRAZY, Type-A, helicopter, win at all costs, my kid should never struggle or face adversity, aggressive MFers. That has included me a few times over the last 6 years of him playing.
The best thing I've seen is coaches who call a parent meeting and lay all this stuff out ahead of the season really getting rolling or if you can't do that, create a code of conduct document everyone needs to sign and return to you that outlines things.
A few best practices I've seen that could help are:
Wait a minimum of 24 hours after a thought crosses your mind before discussing it. Gives the offended party time to reflect and be calm when discussing.
Discussing ice time is off-limits. The coaches philosophy on the subject is... and the desired outcome is equal playing time over the course of the season, not game to game. Or if you are in a more competitive situation... you have to earn your ice time based on the following criteria...
I think getting all this stuff out of the way up front can solve a lot of issues that pop up throughout the season. It may not avoid them all, but at least it will give folks food for thought before they pull you aside steamed up about some perceived injustice. The only place I see things needing to be immediately address is if there is a safety concern.