Throughout its eight seasons, The Vampire Diaries saw many hated and fierce villains, from Katherine Pierce to the Mikaelson siblings. Most of these villains were downright evil and caused chaos and grief purely because they enjoyed it, or it is what they had previously been put through.
Elena was introduced as an innocent high schooler, who was often seen as a helpless victim in the plots of the show, however, there were many moments where she acted in a very antagonistic manner, which she often holds no regrets over either. In many situations, she was looking out for those she loved, but that doesn't always make her actions okay.
Having Damon Compel Jeremy.
After becoming a vampire, Vicki attacks Elena, and Stefan is forced to stake her in order to stop her. Jeremy witnessed the whole ordeal. Damon erases Jeremy's memory and makes him believe she left town, at the request of Elena.
Elena left Jeremy with the false hope that Vicki was alive instead of letting him grieve. Both Matt and Jeremy could have grieved properly had they known the truth. This proves her to be the true villain as she could easily lie to her brother and her friend about someone so important to them and she made the choice to have Jeremy forget without figuring out what he would want for himself.
Drinking Damon's Blood
When Elena becomes a vampire, she struggles has a hard time keeping down any blood. Damon offers her his in order to help her out and she accepts it.
Elena drank Damon's blood knowing that Stefan would not approve. Drinking someone's blood is an intimate act that she partook in, which was wrong of her to do to Stefan. This is a villainous act as she betrays Stefan and goes along with Damon's plan, despite Damon himself being a known villain. This leaves Elena with a taste for fresh blood which leads to her craving it more and attacking innocent people later - and she was likely only forgiven due to both of the brothers being in love with her.
Getting Into A Relationship With Damon
Stefan breaks up with Elena when he senses that she has feelings for Damon. Elena sleeps with Damon the next day.
Elena could have held off or kept away from Damon in order to be respectful of Stefan but instead proves herself to be the villain by instantly going to Damon. Even before the break-up, Elena shared kisses with Damon on occasion when the two were still together, essentially cheating on Stefan with his brother, an action only a villain would do as this obviously causes pain towards Stefan, who has been nothing but good to Elena. This is similar to the actions of her evil doppelganger, Katherine.
Finding The Salvatore Bloodline
If an original vampire dies, their whole bloodline, every vampire they ever created, will die alongside them. Elena attempts to discover which original's line the Salvatore brothers came from to make sure that she doesn't kill them.
Elena knows that her friend, Tyler, came from Klaus's bloodline and that he will die if Klaus does, but she does not care as long as Damon and Stefan are alright - and still goes on to try and kill Klaus. This proves her to be the true villain as she only cares for her own wants and needs, and will allow her friend to die in order to get her way. Elena is also aware that many other innocent vampires will die if she is to kill an original. but again, does not care as long as none of her close friends or love interests die with them.
Killing Finn Mikaelson
Finn has been reunited with his true love and wants to live his life unbothered. Despite Sage being right there and knowing that every vampire he ever created would die too, Elena still attacks Finn and contributes to causing his death.
Not only was this very selfish of her, to kill an innocent vampire and a whole bloodline of vampires who could also be innocent, but she also did not have to do it in front of Sage, who was begging her to stop. Elena had absolutely no remorse as her loved ones were still alive and she got what she wanted out of it, proving her to be the true villain. The impact of this is that many innocent vampires died, which could have been prevented.
Conspiring To Kill Klaus And Kol Mikaelson
Elena was not the one to kill Kol, but she did come up with the whole plan. She decided that killing a whole line of them would be better than only killing a few, showing a very selfish and inhumane side to her, this causes even more deaths that could have easily been prevented.
Elena also conspires with Esther and agrees to her plan despite not actually being on board and lies to Elijah about it. Elijah had always been very honest and sparing towards Elena, and she chose to betray him anyway, she clearly does not regret this as she continues to lie even when Elijah confronts her. This shows her to be the villain as she cannot give Elijah the respect that he gives her, and is only looking out for herself.
Daggering Rebekah Mikalson
Elena daggers Rebekah after coaxing her to help kill her brother, Klaus, by using information she has on him. Elena then tells Klaus that Rebekah was going to assist her in killing him in order to keep him from removing the dagger.
Elena uses both Rebekah and Klaus in this situation, pitting them against each other by manipulating them with the information that she has on each of them. This is a villainous act that impacts both siblings it causes them to doubt each other. She does all of this only for her own gain. Elena could have waited until after the dance, seeing how special it was to Rebekah, but chose to betray her. She also later admitted that she only pretended to care for Rebekah to get her own way, and never apologised to her.
Killing An Innocent Waitress
When Elena turned off her humanity switch, a lot of her villainous actions take place as she loses a lot of compassion with no humanity. Both Damon and Stefan try to convince her to turn her humanity back on.
Elena saw through their plan and killed an innocent waitress in front of them to prove how serious she was about keeping her humanity off. This was a very compulsive and selfish move to kill an innocent civilian just to prove a point and showed a whole new, darker and villainous side to Elena. The impact this had is that a life was lost, Elena did not know this waitress, who could have had lots of loved ones that could miss her.
Lying To Damon For Information
Elena wanted information and knew that Damon could give her it and she lied to him to get it.
This was cruel of Elena as she was aware that Damon had feelings for her and used them against him for her own gain. She lied to his face, making him think that he stood a chance with her and that he would get a clean slate just to betray his trust in the end. This shows her to be the villain as it shows a lack of empathy and she was able to lie to Damon so easily. Damon even compares her to Katherine for doing this, who is a huge villain.
Erasing Her Memories Of Damon
When she believed that Damon was dead, Elena had her memory erased. When Damon did return, it was extremely difficult for him as he had to start from scratch with the relationship.
Elena was selfish to do this as she had lost many other loved ones and had managed to get by, it seemed more like she wanted a quick fix so that she could easily move on without having to grieve another loss, This proves her to be the villain as she causes Damon a lot of pain and only did right by her. The impact this had is that Damon had to try to make Elena fall in love with him all over again as she was never able to remember what they once had, memories that Damon treasured.