If she comes into the fight when everyone's low on health she's going to get a pentakill and there's nothing you can do about it since most CC will be down and there won't be enough time to use it anyways (To a lesser extent
also does this, but at least he isn't smug about it)
Pretty much impossible to catch, has the single worst voiceover in the game, if one spear hits you're pretty much dead. Any poke you land on her is useless because of her heal.
I think fizz was literally designed to be as annoying as possible. He does huge damage even if he misses his ult, he looks like he belongs in skylanders or pokemon or something, and it's near impossible to hit him. The only solace is that his playerbase is usually really bad at the game.
She's ridiculously tanky, does ridiculous damage, and has a ridiculously long stun, all while having sustain and near stun immunity. Her kit has nothing to do with her lore or the fact her blades are floating. She could be wacking people with a skateboard and it wouldn't make a difference and she has the personality of a loaf of tofu. I honestly think she needs a sion level rework, but the whole "better nerf irelia" circlejerk seems to have scared riot away from touching her.
He does too much damage, just plain and simple. His ult is a nightmare clarity wise, you have this big red X on you so you get scared and want to zhonyas or flash or something, but that's useless since it'll just pop you later, that's mostly a problem for newer players though. He's AD so even if he misses every single ability, he can likely still kill you because of his auto attacks. Having to rush zhonyas first item is not, and never will be counterplay.
This is my single least favorite champion in the game. I have not met a single Vayne player that was fun to be around. The only counterplay if your ADC didn't bully her enough early game is to stay out of her weirdly long auto attack range, but she has her passive and tumble to get to you. Even if you set her behind she can still carry late game, it's Vayne's game to lose. Her attack sounds are obnoxious, she's slippery as hell and pretty much impossible to duel. It makes me sad because I genuinely like her concept but it was done in a really bad way.
I know he's not strong right now, but everything about him pisses me off. His kit's design is just beyond awful. His whole gimmick is having two abilities for each slot but there just wasn't any creativity put into it, with pretty much no interesting effects or gameplay. He has the same problem as nidalee, where if he lands a single skillshot then you're pretty much fucked. He outduels most champions, has pretty much every stat in the game thrown into his messed up kit. And his ultimate is just disgusting, it's an undodgeable nuke that can potentially CC your whole team and it makes you travel weirdly slow so you're CC'd for longer. He's tanky and utterly impossible to chase because of his ridiculous dash. His model is ugly and he's blind but that has no impact on his gameplay. Riot is never going to touch him due to sheer player base QQ even though he needs a rework badly. I'm so glad Rek'sai's replaced him.
Honorable mentions
Lands one skillshot and you die.
Has to be kept down, but is also near impossible to keep down.
Spell shield, snare and ult make the game boring for the other team, needs a VU badly
Playerbase is really smug and obnoxious, will usually lose lane then just splitpush forever
You automatically forfeit one of your buffs at the start of the game.
I'm tired so the grammar in this post may be off.