The death of Richard Detmer in the original script. He basically gets his arms and legs telekinetically ripped off by his own son. Yikes.
Similarly, Andrew ripping the spider apart with his powers.
The way Richard actively beats his son is brutally realistic, especially since it outright causes Andrew to go off the deep end.
The time Andrew forcibly removes a bully's teeth with telekinesis. Made worse when he records himself explaining how he removed them.
The time Andrew killed those four neighborhood thugs. It's a lot more mundane than the other scenes, but his callous rummaging of their copses is hard to look at.
Andrew's "Apex Predator" speech:
Andrew: I've been doing a lot of reading, you know? Like, online about, like, just evolution and natural selection and how like there's this thing, right? It's called the apex predator, right? And basically what this is, is the strongest animal in the ecosystem, right? And as human beings, we're considered the apex predator, but only because smaller animals can't feed on us because of weapons and stuff, right? A lion does not feel guilty when it kills a gazelle, right? You do not feel guilty when you squash a fly... and I think that means something. I just think that really means something... *holds his hand out and starts telekenetically crushing the car behind him*