I really hate Mr. Game and Watch ever since he was in Melee. He was definetly the most weakest character in that game, in my opinion. Now in Brawl, there's even more charcters I don't like. I personally have some problems with R.O.B. and Pokemon Trainer. Seriously, it doesen't really make any sense why they're in the game. I mean, the Pokemon Trainer himself doesen't take part in the battle himself, but sends out his pokemon to do it for him, which is really weak in my opinion. For R.O.B., he's pretty much why I also hate Game and Watch, being a weak character.
I also develpoed a deep hatred for Kirby, mainly because people can constantly spam his "rock" attack.