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.
YMMV: The Butterfly Effect
Acceptable Targets: Fraternity members. In the first altered timeline, Evan winds up as a member of a stereotypical group of wealthy, womanizing frat boys who openly cheat on exams and treat their pledges like shit; it's hard to blame his former roommate, Thumper, when he refuses to even speak to him anymore.
Darkness-Induced Audience Apathy: One of the major criticisms of the film was that it was so phenomenally depressing that by the end most of the audience was wishing they could spontaneously commit suicide too. Evan has to cope with being molested by his neighbor, accidentally blowing up a woman and her baby with a stick of dynamite, getting assaulted by his institutionalized father, having his beloved dog burned to death, and watching his best friend lose his mind...and that's just the first half-hour of the movie!
Narm: Any time something particularly horrible happens to Ashton Kutcher.
Or when Tommy, as a kid, beats up a guy twice his size in the cinema after witnessing Evan and Kayleigh (who is his sister, by the way) kiss.
Kid!Tommy in general is flat-out narm, what with his constant cursing and his vulgar MST3K-style riffing on the Gluttony victim from Seven in the cinema. It's like the filmmakers have zero idea how teens behave or talk.
Or when Evan accidentally crushes the granola bar.
Or the deadly serious use of the word "fuckbag" to defuse a child abuse situation.
Or the reaction of the cellmate to the magically appearing "stigmata".
Or the sheer amount of crap in Evan's life even before he starts trying to fix it, which just gets impossible to take seriously.
Or the Stock Scream used by Kayleigh when Lenny kills Tommy in one of the alternate timelines. Seriously, filmmakers, you couldn't have her just actually scream?
Or the...Christ, the whole film.
"Oh, Mrs. Bosweeelllll..."
Nightmare Retardant: The scene where Evan wakes up with no arms. Also counts as hideously painful Narm in some scenes. Sweet Jesus, the granola bar thing.
So Bad, It's Good: Some people consider the film this simply because Ashton Kutcher plays the main character. Whatever else can be said of him, he actually gives a fairly nuanced performance in this film.
What an Idiot: The recurrent "Don't try to change the past" message is somewhat dampened by the fact that many of Evan's woes come from him making painfully stupid decisions that could easily have been avoided if he'd bothered to think them through. He doesn't consider that putting dynamite in a neighbor's mailbox might somehow go wrong; he doesn't think about the possible repercussions of beating a man to death; he thinks that he can permanently stop an abusive pedophile by giving him a verbal beatdown; he doesn't hesitate to hand a knife to a kid who's destined to go insane in at least one possible future...
Evan is molested by Kayleigh's pedophile father, accidentally kills a mother and her baby, lost his best friend (who couldn't cope with the guilt and eventually became a chronically depressed recluse), loses his arms in another timeline and sees his girlfriend connect with the best friend instead until Evan tries to commit suicide (which fails), he suffers repeated brain damage every time he resets the timeline until he's nearly hospitalized as a vegetable, and that's just a selection of his crappy, crappy life.
Kayleigh (along with her brother Tommy) were also molested by her father, and she went through most of the other hardships that Evan faced. In one timeline she becomes a drug-addicted, self-loathing, streetwalker. In another her boyfriend beats her psychotic brother to death in front of her. This is later subverted when Evan ensures that she and her brother will live a happy life being raised by her mother, with no memories of the alternate timelines.