1) Adrian Ivashkov from Vampire Academy & Bloodlines:
I loved Adrian in the Vampire Academy series, and the first three books of Bloodlines spinoff series… But then I realized he’s a promiscuous privileged rich kid who doesn’t want any responsibility and just wants to drink and party. His Spirit use deteriorating his mental health is no excuse to live that lifestyle. The way he acted when Sydney was taken completely disgusted me and ruined the series for me.
2) Eric Northman from Southern Vampire Mysteries:
Eric was super dreamy, then Charlaine Harris did a 180 on his personality and ruined him. 😦
3) Will from Slammed Trilogy:
Will was perfect in Slammed, but in the second book Point of Retreat, he turns into an a-hole. I mentioned what he did to turn me off in my spoiler section over on Goodreads.
4) Rowan from Heir of Fire (Throne of Glass #3 and on):
I liked him at first, then he turned into a moron by the way he practically worshiped the ground Celaena walked on.
5) Grover from Percy Jackson and the Olympians:
At first he was funny, then he just got more and more annoying as the books continued.