I hate Diddy Kong.

I despise Diddy Kong with a passion. He's just...not fitting for the game, IMO.

 This. Well except that I don't use everyone.

I hate whatever character my opponent is using.

Unless it's Dedede. If you pick Dedede to play against me, I'll just sit and laugh because he's just so awesome, I can't even try to fight him.

I hate the vertical scrolling DK stage with a passion!! Makes me want to kill my character off so I can quickly get to the next match.

Oups just saw it was Who do you hate... and not What do you hate... well my answer still stands.. .that's how much I hate that stage!

Diddy Kong is fantastic.

But I really don't like Pit, such a pain!

 Agreed. I don't really dislike anyone in the game, as I use all characters randomly. I do have my favorites, but I enjoy playing with all of them if I have the time. But man, that scrolling DK stage...

I can't stand Snake in a 3 or 4 person Brawl. One of my friends who I always play with just hides and spams Nikita's and his up Smash. I hate Snake. So much. Hate him.

As far as playing...I hate playing as Ganondorf. One of the few characters I'm pretty worthless with.

I love Olimar, he's hard to get used to, and you have to know how to use your pikmin, but yeah^^; I main him.

as for hate? I hate using jigglypuff, I just suck with him, more than other characters.  I don't mind when people use him, if they can they should. I just can't play him lol.