His demeanor. I know you are probably going to say that "it doesn't effect the music" but it does, at least for me. What's up with the random staccato notes thrown in every now and then to sound cool? What's up with looking away for as long as he can to impress people? What's up with making stupid faces as if he thinks the music isn't worthy of him?
I think your interpretation of why he does these things may be a bit off...
I look away (up) from the keyboard often and it has nothing to do with showing off (I have little to show off for). It just makes it easier to concentrate on the physical sensations and the sound. I doubt he is doing it just to impress either. I also cannot always help myself get excited about some spot in the music and add a little to the articulation.
Generally I always prefer calm and poised pianism, but if someone plays that good, then I would just close my eyes and not pay attention if something bothers me. And he is playing for live audience, not YT, so he knows not that much is seen by those he is playing to anyway.
He does not do what so many of the younger ones does, use overstated bodily gestures to make his playing more flamboyant and end up ruining the sound, but instead he lets his face speak freely. IMO His faces and gestures are much less annoying to me than some of the young pianists, because he clearly knows they are ridiculous and is just making fun of himself. And much of what he does still seems to come from his reactions to the music. I also make stupid faces because I cannot help it sometimes. I try not to, but if I was that good I probably wouldn't bother trying

And as I said before, if you hate him, you would have hated the pianists composers that wrote this music. Liszt probably was extreme, but look at some drawings of Chopin, the way he stares at the sky?

But of course if it does bother you it does and you are then right to hate him. There are some that bother me just as much and I cannot watch. But I think my generation is a bit different to yours, since we grew up listening to records and rarely saw videos, so I still concentrate more on what I hear than what I see.