Repeated promises and claims which turn out false.
He is extremely arrogant and annoying. For example used "Pedo Guy" as insult at Twitter toward someone who committed crime of disagreeing with him, proceeded to claim that this does not mean "pedophile" in court.
And claimed that this person "married" 12 year old girl (actually, she was 32 years old).
Also, Musk has bunch of annoying fans.
(that is among some legitimate reasons, many hate him BECAUSE he is successful)
> dozen other things that will save humanity
That is really overstating it, and case of annoying fanboyism.
(personally I appreciate some achievements and see his role in that - without giving 100% credit to leader, confused why people praise some projects already, but see no reason to engage in fanboyism or Musk hate)