Funny how only one name comes to mind and I have to actually think for this one lol. Good thing it's not "which one you hate" since hate is a strong word and I rarely actually hate characters. But here's the five that come to me (in no specific order):

1. Serizawa. He's a truthfully boring, cardboard cutout kinda guy. Though it's not what makes me not like him much (he has the potential to be interesting, hell I even had fun myself writing something about him), but rather most of his hardcore western fan made me not like him lol.

2. Kenji Mitsuura (the institute dude). Not really into him at all, don't mind a "rich dude throwing his money at something he finds fascinating", but not for him.

3. Matsuo. Dunno why, don't feel him much either. But I feel like this one is probably more design-wise, or maybe his voice / the way he spoke too. he doesn't even enter a possible top 50 character I might like.

4. Gonna generalise a bit more, but a bunch of the "scar" group we see in S1. Not saying all of them, since some of them do seem interesting, but most of them I didn't vibe much with really.

5. Another generalisation, but aside from the twin maybe, the kid who studied to make their psychic powers stronger under Kenji Mitsuura.

Honourable mention (kinda): Western fanon Teru. Similarly to Serizawa, his fan makes me not feel him much really. They make him look a bit bland too.

had to look at a list of characters to remember names properly and saw all the characters I just didn't remember, so I guess there's also a rank called "wasn't even worth remembering"