Tough to tell what happened, did not happen, what kind of attitudes were displayed by both sides, without being there. I would not downgrade a person for attitude, nor threaten to deny them boarding unless they appeared intoxicated or violent, and in both cases, I would include local management in the decision (or local police if actual violence was displayed as I have witnessed UA agents get assaulted for doing their job properly.)

First, I question the title of the thread. The man was not confirmed in F, he was confirmed in Y and waitlisted for an upgrade. If the OP is telling the story as it played out, his upgrade cleared at the gate, He admittidly sounded like he was pushy. For admitting his own shortcomings, I tend to believe his story more that the person who claims that they were completely innocent.

The advice given by many is sound. I just watched a girl (45 min ago) argue with the City of Chicago traffic management authorities for 20 min saying that she was allowed to have her own personal vehicle come into the taxi lane (not without a city medallion) without passing thru the taxi booth (where the city collects the useage fee,) It was a no win situation for her. She was arguing with a person that she wasn't going to win with, yet she kept getting all belligerent. Needless to say, she lost the arguement. I think the city worker took extreme pleasure in doing her job and denying her vehicle access to the off limits area.

The difference in the OP's story and what I just witnesed is that the OP apparently did ligitamitly clear the upgrade (again, if the story is factual...I wasn't there so it is just heresay to me) and should not have had it removed for acting like a child. Now if there was a seat dupe and someone needed to be downgraded to their ticketed cabin, that is one thing, but to do it out of spite...well, that is something that I wouldn't do. Sure, I might fantasize about doing that, but while representing the company on it's time and property, my own emotions should be (and are) kept in check. The job is only as stressful as you let it be.

As for calling IM so they don't get an improper CoS bonus. UA's system had functionality that a CS agent could put in to limit the mileage to what was ticketed. Not sure that CO's system is complex enough to do such a thing, so I may be on the phone alot more often