Sometimes, a single scene of FIM or EQG can completely ruin a character for me.  This is something that is not just MLP, but is also affliction to other things and movies like Toy Story or Pokemon.  The reason it can take as little as one piece of dialogue to completely ruin a character for me is because of a thing called character bias.  Character bias is when you like a character so much that you start to base other favorites or least favorite characters around things they have said or done to said character.  For me, I have many of those kinds of characters.  Sunset Shimmer, Ash Ketchum, Peridot, Smolder, and Oscar the Piano are all characters I have character bias for.  Right now, I will focus on Sunset.  Now, I don't like Octavia.  The reason why is because she had that one line in Rainbow Rocks, "I knew she was still trouble!", and because she is a background pony she hasn't been able to redeem herself to me because, well, she's a background pony.  She's not going to get very many opportunities, and she blew one of them.  Next we get to Flash.  I don't hate him for being a love interest for Twilight, although now that I have had a taste of that medicine, I honestly can see why so many people hated him.  It hurts to find out that the character you like really, REALLY likes someone else.  But I don't like Flash because in RR, he not only made Twilight CRY, but he also STARTED the outburst against Sunset after she knocked over Rainbow Dash.  And no, he's not completely under the Siren's spell either, because remember in "Under Our Spell", Bon Bon and Lyra are holding Muffin back from fighting Bulk Biceps, and they looked concerned for someone.  It doesn't matter who, because neither Bulk or Muffin is on their Battle of the Bands team, so Flash is definitely partly to blame.  Principal Luna, where do I start with you?  Not only did you place an insane amount of stress on Sunset in FG, but you also made a really unfair and hurtful statement to her in RR to deflect her accusation of the Dazzlings, and, you shut down the dock in LOE because of ONE BROKEN BOARD!  I just genuinely think Vice Principal Luna is not fit for the job of Vice Principal, but her role in RR and FG doesn't help her.  Snips and Snails were never contentious characters for me until I watched Sunset's Backstage Pass, where

And combine that with the fact that Snips and Snails are the most obnoxious little people ever in EQG, and Snips is so annoying in MLP, and the only one of the four who comes out with no hate from me is the MLP Snails, because buckball saves him.  Last for now, we have Wallflower.  I hope we never see her again.  She targeted Sunset because, why?  Sunset didn't remember her because Wallflower erased the memories people would have remembered about her?  Sunset ignored her like everyone else?  Why target Sunset specifically????  And then Wallflower gets forgiven instantly and receives no punishments.  You don't target Best Pony and get away with no consequences and expect me to feel sorry for you, especially when you caused this for YOURSELF!  Stop blaming Sunset specifically for something she didn't do!!!  Wallflower just makes me mad.  Do you ponies have any character biases?  If so, feel free to tell about them in the comments below.