In every game I played that had a Vayne, that Vayne team wins. I don't get the 'feeding' joke, does it have to do with her passive? I assume one would just use her Tumble/Q to move left or right or in the occasion of catching up to an enemy.
From trying her out I didn't see much bad about her.
A great vayne can snowball like crazy and can 1 v 3 or even worse when fed.
A bad Vayne is super duper useless.
Very, very polarizing and thus seeing her selected strikes fear in your heart no matter which team she is on.