Just his general attitude towards humans really. He keeps bringing up the nastiness in their past (constantly forgetting about the nastiness in the Vulcans' pasts) like they're the worst.
You're gonna have to to better than that. Where does he say or at least imply that Humans are the worst species ever? And as I said before, he's quite willing to discuss Vulcan's nasty past.
You have watched TOS, right?