[SIZE="a"]Well I'll give a few for every generation
Generation I- Zubat and Tentacool. Those two Pokemon are the reason why I buy repel.
Generation II- Jynx, Dunsparce, and Whitney's Miltank. Jynx is just.. Terrible and Dunsparce is pretty useless and Miltank isn't really hated just specifically Whitney's Miltank because of its Rollout attack.
Generation III- Zigzagoon and Seedot. I don't see why people hate Zigzagoon it's useful in the beginning part of the game. It will pick up a few useful items using it's ability that would otherwise be unattainable until later in the game. Many people don't like Pokemon based on imadimant objects. A lot of people consider this to be the generation when designing of Pokemon went bad. The designing style changed for sure but it's an opinion on whether the designs are bad or good.
Generation IV- Bidoof, Lickilicky, Probopass (and other new evolutions). Bidoof is the typical beginning of the game useless Pokemon. Lickilicky and Probopass are new evolutions introduced in this generation and many think the designing of these two are flat out terrible.
Generation V- Woobat, Lillipup family.
Woobat is the Zubat of Generation 5, but worse. A lot of people say that Lillipup is a symbol that the originality of Pokemon is no longer there since they are based on dogs. What's funny is Growlithe and Arcanie are very loved Pokemon, they are based on dogs as well.[/SIZE]