Episode 2, "A Lie and a Truth". People who were trolled or scammed online and nearly paid their lives for it will understand.
In the episode "Takes A Sudden Turn", during a forum Saika induced victims start posting various disturbing comments, and the "trolls" can't be blocked off the forum. Suddenly the comments from the trolls start to rabidly post the same comment over and over while Kanra and all the others on the forum are noting its creepiness factor. What did the comment say? "Mom. Mom. Mom. Mom. Mom." This was going on while Anri was getting beaten up by several students. To make matters worse, the Slasher shows up....
Shizuo's rages. We're talking about a guy who can lift vending machines out of the ground with ease. And when he is having a particular bad tantrum, he tends to throw heavy objects into the street, which more than likely has either killed or injured random people.
The worst part of it, in the anime at least, is that while Erika and Walker are getting ready to do their thing, they're told not to use gas in the back of the van again (implying that they've done that at least once, and probably more times than that, if there needs to be a repeated warning). And they start brutalizing some poor schmuck while their friends just stand off to the side and drink milk.
Ran Izumii. He's threatened at least two women with rape, and it's heavily implied he raped his little brother, Aoba.
When Seiji suddenly smashes Mika's face against the wall when she takes a glimpse of Celty's head.
Mika ends up getting plastic surgery to fix her injuries... and makes herself look exactly like Celty with her head on. Can we say, yikes?
And then, after it's revealed that Mika is in fact Seiji's stalker and not a human body with a different head attached to it, they stay together even though Seiji keeps telling Mika that he's only staying with her because her face looks like the random head he found so many years ago, and that if he can be reunited with it, she's history. And she just eats this up for some reason.
If going by the anime, Seiji himself knows this. And he's totally okay with it, too. On the upside, it does seem to imply that their relationship is a genuinely happy one. Or that Seiji has Stockholm Syndrome.
A young Namie taking showers with Seiji is sickening. Her incestuous love for him is horrifying. We're talking about his own SISTER, who grew up taking care of him, and she actually wants to shatter his trust in her by making babies with him. Talk about mentally scarring stuff here....