It's hard to find something to dislike, let alone hate, because for everything you think you hate, there's honestly an alternative. Don't like the fact that the general Pokemon stories are bland as heck? Play one of the console games. Don't like that Pokemon are only seen as kockfighters? Play one of the side games. Don't like the side games or the treatment of the Pokemon? Watch the anime. Even fans can be ignored by and large (and if they get under your skin, you're giving them too much power).
I feel like at best you can only describe gameplay values, such as hating how much Chansey keeps running away from you in the Safari Zone without fail.
I dunno, I'm just so neutral about everything, but that's just my personality. No reason to find things to dislike.
But just to play along, the thing I "hate" would be... um. Oh, okay. I don't like it when spinoff games have a different artstyle for everything but the Pokemon. That's so very dull. Even Mario gets an artshift, and he's the plainest long running everyman protagonist there's ever been in a video game.