When a Yasuo takes 80% of your health in true damage by point-and-clicking you
Really this champ makes absolutely no sense right now. Armor penetration on his ult feels like a sad joke now, in no case he ever needs that.
He might even not be that strong right now (because the same changes that gave him retarded amounts of true damage reduced his burst against squishies, hurting his teamfighting seriously) but after 2 items he just gets to point-and-click you to death regardless of items, landed skillshots and whatnot.
If you don't happen to play a very strong duelist yourself, you will spend later 70% of the game doing nothing but pushing him back, as close to the tower as you can afford to stay. You can never fight him, regardless of how many Q's you dodge, and he has no incentive to group until super-late.
He really reduces the game to a coin flip of who's teammates do better.