Good heavens! Where's my popcorn?? *Sits back to watch the thread evolve*.
If Mr. Parelli wants to deal with his horses this way, more power to him. His horses, his party. If the owners of the horse are content to watch this carry on for the 2 hours described in the clip, that's their affair. That being said, call it what it is; it certainly isn't "love, language, and leadership". If Mr. P did that to my horse, I'd show him right where to put that carrot stick.
I've personally bridled horses, just seen a small kid at a 4-H meeting with a tall horse and ask if they needed help, slid the bridle on piece o' cake, and had the kid tell me that the horse had never been bridled without a twitch and a panic attack before. Perhaps there is a time or place for twitching/hobbling/whatever-the-heck he was doing, but it does look like a pretty darn harsh reaction for the simple "don't touch my head" evasion.