I was referring to ignoring the fans in the stands. As has been said on here, nothing good can come from arguing with them. As for a coach, if he is getting out of line, I'll let him know.

Me (after hearing a few remarks from the assistant coach): "Hey coach, muzzle your assistant or it's going to cost 15"
Head coach: "OK"
Assistant coach: "Muzzle me??? mpfhmpfhmfhmpmfhp" (Sounds emanating while head coach has his hands covering the mouth and pulling assistant away from me)
Players: Laughing uproar
Me (wondering): What a beautiful sound. :D

I've found it's usually not a good idea to embarrass a coach in front of his players. You're never sure in what direction that might take you. However, I see no problem in quietly, and calmly, advising the coach as privately as possible that he has a choice. He can mind his manners and keep his comments to himself, or he can choose to say whatever he wants as loudly as he likes in the parking lot.

It's his choice and it's irrevocable.

Ignoring and communication.

I'm an official who works for the Danish American Football Federation (DAFF). I was working white-hat at a 4-man crew in a 9-man football game. On a running play off tackle (TE) the ball-carrier was "trippet", meaning fell over a defensive linemans leg (did not go down, but could keep running). Offense sideline yelled out "TRIPPING!!" but I simply replied "no!" and continued officiating; whereafter the sideline went silent.
After the game one of the coaches over and said "You had the comment of the game.." with a smile on his face. They had accepted that I had seen the action, but knew that it wasn't a foul (contrary to them).

At the same time when you have the split-second decision "think-through" time that was discussed earlier, and decides to throw the flag just as a coach yells in you head, that there is a foul I usually reply "I HAVE seen it ,coach!" in a tone that says "back off".

As you can see in my clarified posting, I wasn't setting out to embarrass the assistant. In my sitch, the head coach was very cordial throughout the game, while the assistant had plenty to say (nothing bad, just incessant chatter about this and that which I usually don't listen to until it becomes personal). He just finally pushed a nerve when he "decided" he would ask why I didn't flag something. That's when I told the head coach to muzzle the assistant before it hurts the team, especially when it was a freshman game. How the head coach decided to muzzle him wasn't my business but it was quite amusing.