These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Complete Monster: Takao Hiyama, The Third Diary User. Notably, because he's the only evil person that continues his killing sprees with and without the diary, he's the only character who does not get a happy ending, unlike all the other diary users in the third timeline.
Yomotsu Hirasaka, though that's kind of inevitable for a blind insane Super Sentai parody.
Crosses the Line Twice: Takao Hiyama appears in a flashback in the middle of one chapter... only to take a spear in the back, courtesy of Yuno. Him being an Asshole Victim is probably what makes it so funny in the first place.
Yuno crosses it when she lies to Yuki and convinces him to kill his friends, all of whom were only trying to help him; she even delivers an Evil Laugh when she learns about Yuki shooting Hinata.
Tsubaki crosses this when she orders her followers to strip off Yuno's clothing... and to gang-rape her, all so she could lure Yukki out of his hiding place.
MurMur crosses this when she undoes the positive future in Paradox by deliberately erases everyone's memories and goes back in time to make sure that the 2nd is still alive and kills them all. She also uses the wounded Yuki to prevent Akise from stopping her plans.