It breaks my heart when I see my favorites listed :*(
I try not to hate cartain Pokemon too harshly. Usually when I hate a Pokemon, I manage to find something good about it. Anyway, here is my list.
Kanto
1. Eevee- despite being part of my username, I really can't stand it. It's the fans mostly. Eevee fans tend to dislike the humanshape Pokemon I like because they're not cute and cuddly enough. Poop on you Eevee. Come back to me when you evolve into one of your kanto evolutions.
2. Mewtwo- similar to Eevee, it's the fans that make me hate it. "Oooh, Mewtwo is so deep, he's the only Pokemon to have a deep story, I can relate to him", blah blah blah. Mewtwo's design is cool, that's it.
3- Snorlax- Gee, think they put enough effort into making it a pain to battle? High HP, high special defense, high attack, and with curse it's uber. I so wish they gave Snorlax the truant ability.
4- Zapdos- I really don't like its looks, and its type combo makes it hard to defeat. A rock/ground type can easily take it down unless it has stupid hp grass/ice/water. Silly big bird.
5- Any Pokemon with static or poison pin- I like Nidoking and I like training Pika/Raichu and Electabuzz, I just hate fighting these Pokemon. My Pokemon seem to get the status effects 90% of the time.
Johto
1- Blissey- Words can't describe how much I LOATHE this Pokemon. It's... ugh... high hp, high special defense... and that design! Let's make Chansey, a tolerable Pokemon, even more disgustingly feminine and raise its already godly HP even more.
2- Pichu- It's a bunch of colored circles slapped together.
3- Igglybuff- It defeats the purpose of being a cuter Jigglypuff by being downright creepy looking.
4- Jumpluff- this Pokemon is only good in competitive play. Ingame, it's almost useless. I just have horrid memories of training Hoppip up so many levels, thinking a grass/flying Pokemon would be worth it. I was wrong. They should have left the Hoppip line out of Crystal and put the much more useful Mareep line in.
5- Anything super weak and pointless and boring- I'm mostly indifferent to the Pokemon that fall into this category, but whatever.
Houen
1- Slaking- Same reasons another said.
2- Jirachi- way too cutey cute for me.
3- Kyogre- or shall we call it Kyuber? Hey, here's an idea! Let's make a powerful water type have high special stats, auto rain dance, and the ability to learn thunder and earthquake!
4- Feebas- why not just Magikarp evolve by beauty instead of making a new Pokemon who looks exactly like it?
5- Cascoon/Silcoon- similar to Feebas, it's ignorant that they make Pokemon who are pretty much exactly the same. Just make a single cacoon have a branch evolution.