I agree with everything you said if you are doing adult games. But this was a YOUTH game and teenage girls were around the coach when he talked to me.
Lets look at what options you have: 1) did you feel personally threatened (doesn't have to be bodily harm, can be any type of threat) by the coach's words or actions? If so, red plus possible report of referee abuse. 2) were his words or actions just offensive or abusive (foul language)? If so, simple red. 3) were his words or actions merely dissent? If so, simple yellow. It sounds in this instance like you had situation #1. I recently had the pleasure of dealing with a situation like this in a state tournament (think I discussed it in the best of 2012). The coach's physical demeanor and behavior prompted an ejection and report for referee abuse because of his threatening behavior.
If you ever have to question if the facility/administrator of a league is going to back you up on something like this because he is trying to protect his business, you need to stop working for them. We enable people to have the kind of leagues by being there to provide a service that others don't want to do and then we take all the grief we normally do and have to do it under the assumption that we are not respected as much as the guy refilling the soda dispenser at the concession stand. If the facility manager wants the games called that way. Let them do it themselves and the attitude might change. There are always players wanting to play, there aren't always referees willing to ref.
A facility around here went through this phase as well. "The players are the paying customer, find a way to keep them happy." They soon found out that the other team in each of these incidents is also a paying customer, and they didn't like paying to play against a bunch of whiny, abusive douchebags. A couple of teams were asked to take their business elsewhere. The place now has so many adult teams playing that they've had to de-emphasize youth leagues. And the refs and teams are told that behavior that is inconsistent with the goal that "players are here to have fun and work up a sweat and go home uninjured" isn't welcome. Business is booming.
I am fortunate enough to work at an indoor facility where the owner is 100% behind the referees. He emphasizes that all the FIFA laws applies (expect for his own modifications for indoor play). There have been many instances that players have been shown yellow and even red cards for bad behavior, dissent, or foul language and the owner will insist that any subsequent suspension is followed through or the team is disqualified from league play. And business is still booming there.
While it would've been nice to have actually been there to witness it and get the full context, from what you said... Yea it was enough, he was being an ass, and its that sort of irresponsible behavior that only grows more irresponsible over time if you let them keep at it. nipping it in the bud now saves a lot of trouble for later. I like preventive refereeing that not only prevents stuff from happening in your match later on, but also prevents stuff from hopefully happening in other matches. mho
Absolutely. At that point, the red card is meaningless, either as deterrent or as punishment, if you don't report it.
Stick with it. From what you said, he is a classic bully. He is likely this way anytime things don't go his way. You aren't the first ref he has tried to intimidate. Really loud and pounding his chest. the minute you stand up to him, a sniveling, pleading brat. Backing down would only be empowering him again. Do yourself and every ref after you a favor and keep the balance of power in check. As for sufficient cause, based solely on your account of the situation, yes. It was sufficient cause for dismissal.
Report the card, report exactly what was said without offering an opinion. If the card is issued it has to be reported, if you as the referee felt you erred, then put that in the report. You will gain more respect by reporting and saying that maybe you were wrong than you will by not doing your job and not reporting it.