OG, it is hard to impress coaches for playoffs when you are working subvarsity... but that is a good point to note, and something I should have included originally.
I think in my career, there are only two times that I probably should have flagged a coach, both jr high coaches. And much like when you are in a heated exchange with someone, not related to football or officiating, and you think of something you should have said about 10 minutes after you should have said it? In both cases that's what I felt about the coach flagging in those situations. At no time did they cross the you line, you know... you suck... or you *#($#(. It was more of an insinuation that we (i just happened to be on the sideline) were making calls simply to favor the other team, in one case.... In the other it was just a continual barrage to the point that he wasn't coaching the team any longer, but was more concerned with coaching me (this was very early in my career) made even worse that in this district for some odd reason they allowed the coaches to be on the field during subvarsity games like it was a scrimmage.
So in the first case, he was basically insinuating that we were cheating... which was funny because 2 of the 3 officials in the game actually lived in the school district that he "represented", this was probably my 3rd year calling and I let it go, should I have flagged him, probably, did I think about it right at the time, no... did I think about it after the fact, yes... Hindsight is always 20/20, but at the time, yeah, his chatter didn't impact the game it was just in my ear... so I ignored it when I probably shouldn't have...
In the second case, it was my first year and as noted, they had free roam of the field... so he was in my hip pocket the entire game, being very green didn't help matters, but at the time I really didn't know what to do, now I would handle that situation entirely differently, but again, it was him, his district basically said that they could go anywhere, carte blanche, but he very well could have been FOS as the other coaches stayed in their area the whole time, even though I was on the visiting sideline and he was there with me part of the time.
That is part of the seasoning of officials, to handle those situations correctly, especially when it comes to sideline control, both of those situations would be handled much differently at this stage of my career than when they happened but that is life, you learn from your mistakes and you try your darndest not to make the same mistakes again... Other than those two occurances, I can't think of any time where I didn't throw a flag on a coach when I look back and think that I should have, for the most part coaches are pretty good, they get heated from time to time and they would be quick to point out that this is their livelihood and is just our avocation, and I would imagine if my paycheck depended on how kids from 12-18 played athletics, I would probably be a little more on edge as well.
I heard on NCAA college supervisor put it in these terms for officials.... "Be the calm in a sea of chaos, maintain your poise, always"