Parent tantrums are the easiest thing in the world to avoid. First of all, when you’re at a real impasse you should just do what they parent asks. They’re not our children. But sometimes parents ask for this that are just not possible. If they get unruly then you let them go. They can’t come meet with you at the school without permission, and you don’t have to respond to their emails or phone calls when they’re getting ridiculous. The minute they become unreasonable, all you have to do is tell them that if they’d like to continue communicating they’re going to have to make an appointment to come see you at the school. If they do that you make sure there’s someone in the room with you when they come. They hardly ever come. Then they can come get it out of their system for a half hour while the administrator or the counselor or whoever you have helps deflect them.
This is a skill that comes with time. You just don’t have to argue with parents unless you choose to.