Mordekaiser? Diana? You'll be fucked. And LeBlanc will get fed if you play as Akali vs LeBlanc. And a couple of patches ago it made LeBlanc perfectly able to come back in the game without being fed, hence some play her as support.
To be fair, I often hear people bang on about "This champion is OP once fed" which is pretty fucking stupid.
The majority, not all, of the champions on LoL are OP once fed, it's just the hyper-carries that are the biggest pain in the ass for obvious reasons. But like @Wess said, people like Akali, LeBlanc, Annie etc are all classed as hyper-carriers imo (not sure on any of the others).