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.
Les Yay: Rebekah and Cami at the bar in "Tangled Up In Blue".
A lot of people remarked on Rebekah and Hayley's great chemistry as soon as the former joined the series (probably helped by the actresses being very close friends).
Magnificent Bastard: Celeste, a master of the very long game which somehow completely avoids any feeling of Xanatos Roulette. However, this is ultimately subverted in Episode Fifteen when she is Out Gambited by Elijah and proves to be a Smug Snake bent on petty revenge against him for something he didn't even do.
Between the witches and the originals it's all one big battle of who is the bigger magnificent bastard.
And as of 1.21, the winner seems to be Francesca Correa, the supposed leader of the 'human' faction, who turns out to be descended from a werewolf bloodline thought to have been extinguished by Marcel in the 1920s. By the end of the episode, her family is in possession of the black kyanite stones that prevent them from turning in the full moon (at the expense of draining Klaus' strength thanks to Genevieve), every vampire in the Quarter has been poisoned with werewolf venom and she's all but taken control of the werewolf clans to take back New Orleans.
The season finale shows that she shares that role with Esther Mikaelson, who had taken control over the ancestor witches and used her power to get the witches to go after her children and granddaughter.
Moral Event Horizon: Klaus daggering Elijah was still a pretty powerful scene. Topped off by Klaus's reasons as to why he daggered him.
Agnes for brainwashing Camille's brother to go on a killing spree and all of the witches except Sophie for slaughtering three innocent girls, including Sophie's niece, and trying to kill Davina as well.
It doesn't take a whole episode after Monique is resurrected before she kills Sophie, the very person who has spent the last 8 months of her life devoted to finding a way to save her. All Sophie did, she did for her and the other girls, but mostly for her. It paints her role in the story quite clearly.
Genevieve and the other witches except Davina for deciding that it's somehow a good idea to kill a newborn baby as a sacrifice and would have gone through with it if Team Klaus hadn't stopped them. It's at this point that the witches and the ancestors cement themselves as completely evil.
The show even managed to do this with The Originals as they were a Base Breaker in The Vampire Diaries.
Pretty much anyone who was a scrappy or a base breaker on The Vampire Diaries tends to get rescued once they jump ship over to The Originals.
Once her backstory and motivation for returning to New Orleans (a.k.a. being in the show) were revealed, the audience even began warming up to Camille. The fact that she is also currently being used as a compulsion spy/mind puppet by Klaus may have also helped.
The Scrappy: Monique is by far the biggest one, mainly for killing her own aunt, Sophie,. While not a popular character, people definitely weren't happy to see her die like that. However, her attitude after coming back from the dead hasn't helped. She's shown very few redemptive qualities and has spent most of her time antagonizing the Original family and bullying a fairly popular character.
Tyler has people wishing that he stayed in Mystic Falls.
He's basically a base breaker for some people who believe that he has improved or is geared for improvement since his introduction.
And it got worse when he went back to the parent show as his Scrappified self.
Squick: While Marcel and Rebekah have chemistry, the fact that she helped raised Marcel since he was ten years old and then was about to have a very adult relationship with him when he reached adulthood makes it come off like this. It seems to border on incest between a favourite aunt and nephew...
The one-sided Incest Subtext between Rebekah and Klaus is considered this.
What Happened to the Mouse?: Inverted. Tyler's return to Mystic Falls isn't so much as mentioned on The Originals. It's revealed on the main show, The Vampire Diaries, but the viewers who were no long watching Diaries had no explanation whatsoever as to what happened to him