I know I'm gonna get a lot of flak for this but I'm gonna have to say Piplup.
My disdane for this Pokemon stems primarily from the anime and how infuriatingly annoying Dawn's Piplup was. Most people fawn over how 'cute' it is but in my opinion, if you have to try that hard to make people notice how 'cute' you are (I refer to all of its so called antics), then all you are being is a massive attention seeker. As a character trait, this is repulsive to me.
For something to be considered 'cute' in my book, it has to be genuine; the cuteness has to be subtle. For instance, take Ash's Cyndaquil and Totodial. Cyndaquil was introverted and it had to learn to be more brave. How the anime handled this gave Cyndaquil a certain charm and endeared you to it. Totodial, on the other hand, was very curious and enthusiastic. It's enthusiasm was genuine and infectious and it was handled in such a way to give Totodial a certain charm and endearment, like Cyndaquil.
Like I said, deliberately trying to make oneself the center of attention is an ugly character trait to have. It was seen in Ash's Chikorita/ Bayleef (but to a much lesser extent) and I find now even more so in his Oshawott (which the writers seem to want to make into an exact clone of Piplup).
If you find these characters as they are to be adorable, more power to ya. They just don't seem to work for me at all on any level.