I will list mine in terms of Generation and Occasion.
Gen I: Zubat, Slowpoke+Evos...just eww..
Gen II: Quagsire (annoying as hell), Dunsparce (its forgettable).
Gen III: Almost all of them, idk why, it might sound unfair but I didn't favor much of them. I hated Zigzagoon, Lotad, and so much to mention, they don't look so colorful to me sorry :(
Gen IV: Bronzor+evo (That things is sooo annoying!!), Bidoof+evo was forgettable as well. Hippowdon and Gastrodon, they're a pain to take out, oh drifblim too.
Gen V: Almost all of them as well, yet I am impressed by some of them.
By Occasion:
-Slowbro: I hate this thing at a battle subway! Too hard to take out!
-Whiscash: Same reason as above
-Quagsire: Same reason as above
-Drifblim: Same reason as above XD
-Ludicolo: So annoying when used well against you
-Zubat: That thing kept following and popping up from the beginning of PkMn till GEN IV. Screw this thing!
-Jigglypuff: Soooo Feminine, much more useless. Actually, the main reason I hate jigglypuff is because my sister keeps annoying me with her Charm -_-
So much more to mention but these are basic.
I do not hate Magikarp though, that thing was so funny haha XD
I am glad to let it all out....Thnx for this thread. :)