I'd've been spitting feathers with annoyance over this - it is entirely unfair of the parents to have put the other passengers through this.
Even if the child has an illness that makes him mental, there are ways to manage things like this - the parents have utterly failed.
Trouble is there are so many parents who smile indulgently when their kid is being annoying because they think if the little darling isn't getting on their nerves then how can it possibly be getting on other people's nerves - simple, it's your kid, not mine. You may not find it annoying, but other people will.
I was always very conscious of my kids getting on other people's nerves, and therefore if, for example, they decided to kick-off in a shop, then I'd remove them. I appreciate you can't do that at 36,000 feet, but if does beg the question why the hell are they taking a kid who can't behave on an 8 hour flight?
From the video "calm down hunny" - I suspect that is the limit of the parents way to control the brat.