People mix up Toxic and OP a lot.
Or is that just my opinion? I hear a lot of people raging about how insert champion is toxic and needs to be nerfed ASAP, but then I look at the stats for the champion and find they're quite average. Now, for me, this is MY opinion, Nidalee, Vladimir, and Swain are toxic champions to play against, because if you make one wrong move, you get punished so severely that you either die or have to back, or after you combo them and try to walk away, they heal up 2/3 of your damage and chunk you for for most of what you just did.
And yet that's the point, that's the theme behind them at times. Sure, it's hell to go against, but you have to deal with it. Sure, you probably can't 1v1 them, you don't need too. (Unless you're an assassin, then you're kind of fucked, sorry bby.) You have a team, use that to your advantage. If you're in mid lane and nothing is really happening, and you're a champion that's viable to roam, you roam. You get your team and yourself fed through other means, and you make sure to keep tabs on the champion that was in your lane so you can make sure they don't roam.
Probably OP because she wins more than she loses and seems to have some pretty powerful stats, but nothing about her is inherently anti-fun. 
is toxic because whenever she is the slightest bit viable people hate on her vehemently, mostly because a single mistake can cost you massive chunks of health, your life, your lane, and possibly your game, whereas her mistakes are easily rectified.
and 
are so OP is because people don't take ignite. If you aren't taking healing debuffs against regen champions... well you are just helping set them up to succeed.
is toxic because her early game blows, making it incredibly frustrating to have her on your team, but IF she is able to reach her late game, you can't do ANYTHING to stop her from killing you, making it very frustrating for the enemy team.
, this person is somebody I find toxic to go against. She can be shut down, but if you're playing a melee champion, even with a gapcloser, if you don't have super burst or hard cc on a short cooldown, you'll be hard pressed to escape or kill her. That's her design, and so many people hate it.