Main offense: It has boobs!
What went wrong: Guys like boobs. Guys like Pokemon. But sometimes two good things just don't go together. Take Castform, who's an otherwise decent and cute Pokemon, but is rendered completely creepy by the addition of weird, boob-like things dangling from where its torso should be.
Lesson learned: Pokemon are already cool enough on their own, they don't need weird boob-like appendages to make us like them.