Well imagine if your kids are swimming around the back of the boat and the jetski comes around the front. So yes, it's obviously dangerous. It is also illegal and ignorant.
The 5 knot law applies 200m from shore and 50m from other vessels. Clearly this guy doesn't know, doesn't care, or both.
And to calm down those who would suggest murder would be a disproportionate response, I'll spell it out: the topic post was tongue-in-cheek. Take a breath.
Breaking legs - too much?