Before you Princess Bubblegum lovers go on and go hating on me, I would just like to point out that this is my opinion. Please be respectful about it. Also, I am making this article because you might see me hating on PB for no reason, but I do.

Now, where do I start? Ah, yes. With her science obsession. Princess Bubblegum is just so fucking obsessed with science that she does not even give time to those who need her. I am not also a big fan of the Science subject so I am not amused at all with her character.
If I can remember correctly, she was so obsessed about revenge and her complexion in The Duke. She did not even BOTHER to know why was the reason why The Duke of Nuts was eating all of her Royal Pudding. The Duke of Nuts is a nice guy. Just because he ate all of your pudding you immiediately accuse him of throwing a bottle on your face turning you green and bald?! I wanted to STRANGLE her!
Also, in Incendium, Finn was trying to make a romantic advance to her and she just REJECTED HIM like nothing happened between them when they were both 13! I wanted to kill her then! She made Finn look so weak! I was always a fan of Finnceline but I also gave understanding to Fubblegum. She was acting so bitchy then. (Please note that also like Flinn, but not as much as Finnceline)
Plus in Wizards Only, Fools she gave no absolute RESPECT to those wizards! She was close with the Grand Master Wizard, but what is the use if you do not even believe in magic?!
Plus another flaw is that she is WAY to girly. I hate girly-girls who are such mary sues! She is too perfect to even know her strengths and weaknesses.
AND, In the Suitor when Braco was trying to court her, she treated him like dirt! If she just told him her plan she would not have had a physical defect!