The implications that Granddad's whipping of Riley has caused him to develop the personality that he has. It's actually very terrible if you know someone who was messed up through mental/physical scars by belt lashings.
The whole episode of "Smokin With Cigarettes". Normally, this show is a political satire, a comedy and an action/slice of life show. This episode is about the exploits of a sociopathic child named Lamilton, who mercilessly hurts and endangers people because he thinks it's fun. "I like doin' bad things," he says. His eyes are dead, totally devoid of emotion. His childhood was traumatic and abusive, but he is a completely unsympathetic character. He claims that he wouldn't care if he kills the people he hurts, and he means it. Even Riley - the boy who idolizes criminals and killers - thinks he's a monster. Lamilton causes countless car crashes, punches people, tries to rob an old woman, actually shoots that old woman's dog to death, and tries to kill Riley!
You want to really have a reason to stay up all night? There are real kids out there just like him. They're just limited in the damage they can cause because they don't live in a cartoon.
He's actually based on one of those kids, specifically Latarian Milton.
Also, when Lamilton falls off the school building in the end, he just gets up and walks away. Yes, he is apparently immortal!
Stinkmeaner is this and the series' evil incarnate. Even DEATH cant stop him, he'll just keep coming after you.
The entire scene where he comes home to Sarah in Tom's body, and you don't see his face. And Sarah doesn't recognize the obvious difference in his face.
Uncle Ruckus suddenly becomes one in the episode showing his origins. He's a black man who has been broken down to such an extent that his entire existence has become a hideous mockery of the old black "Uncle Tom" stereotypes. His cruel, abusive father traumatized him so badly that he hates his own race. This gets even worse in one episode where he founds an entire church based on getting black people to hate themselves. The man is so incredibly mentally broken that when he's told via DNA testing that he is '101% black with a 1% margin of error', he completely loses the will to live.
This especially applies to him when he goes from relatively harmless to dangerous.
The fact that the Booty Warrior is based on an actual person, an actual inmate named Fleece Johnson, is rather unsettling.
Ed Wuncler Jr. While his son's sociopathic tendencies are at least amusing, he's rather... unsettling. Probably because while his sons criminal behavior is destructive, he's basically too stupid and reckless to really be considered evil, he's little more than a product of gangsta media, Wuncler Jr knows exactly what he's doing, and is very good at it. And unlike Ed Wuncler Sr who's at the very least not particularly evil, just super greedy, Jr doesnt even seem to care that much about money, he just gets off on having other people's lives in his hands. Anyone with even a passing knowledge of psychology can probably tell why this is a very, VERY bad thing. At one point his valet even tells Robert to do anything, even fake his death, just go get away from Wuncler.
The flashback of the racist townspeople attacking the Freedom Riders.
The entire concept of Freedomland: A slavery amusment park attended by people who don't seem to care just how horrifying the concept is and staffed by people who are so far in debt to Ed II that they're forced to work there in rather degrading circumstances. If that wasn't bad enough, the staff is also forced to live there, living as actual slaves did.
Ruckuss is paticularly horrifying in this episode. The sheer amounts of joy he gets and his refusal to listen to how insane he's being are rather horrifying.
Ed II trying to cut Huey's foot off.
Ed II trying to branch Freedomland.
Everything about Robert's digital phone assistant Siri in "I Dream Of Siri", from being able to hack his accounts and Facebook page and even being able to mimic his voice in order convince the government that he's a member of Al Qaeda, resulting in Robert almost getting killed by a drone strike.
The idea that anyone would want to clone Stinkmeaner.
Asshole Victim or not, the two hair product dealers burning to death in Roberts mobile home/hair product lab.