I'd have to say that we have an ethical obligation to say nothing that is given to us in a game situation to another coach. You learn to take most things that a coach says with a grain of salt. If there is an issue with repeated violations that they saw in film, you certainly want to be aware of it. But, you shouldn't let guide the way you call that game and you don't want to mention it to the other coach.
On the second point, if any coach gives you a bad eval grade, the league, etc. should require that they justify it with an explanation. If it's his opinion on judgment, that shouldn't be given a whole lot of weight, especially without video support. Rules questions are often more cut and dry, although we should certainly have a leg up there. Mechanics - Well, a junior high coach commenting on mechanics? Really?
That being said, the one thing that can get you in trouble is attitude. That's something that everyone is willing to weigh in on. A poor attitude on the field will get you in trouble almost every time. As will, too much talking. Try to keep discussions short and to the point. I have seen a lot of older officials get themselves jammed up over the dangerous combination of a poor attitude and the need to verbalize it.