Can't post one of these without gettin flamed ;D

I would know trolololo

Vayne has little potential to be an off tank, unless she sacrifices a ton of her damage for tank items. Personally, I find either 1 of the 3 survival items more than enough to stay alive, and the one I'll usually pick is Frozen Mallet.

The point of being a Carry is to dish out damage, not be a semi-tank unless your skills allow you to.

If you notice pro Vayne players, they have few deaths and lots of kills. Your particular Vayne would have more deaths and less kills since your damage isn't too good w/o much offensive items (Carries usually are item dependant).

For your info, Trinity doesn't stack with Lich Bane and frozen mallet's passive.

Hope it helps :)