When you have a fed team-mate ...

{quoted}

depends on the champ. if he was that fed and had the ability to carry, he would have done it already (in most cases) if the fed teammate is say, vayne, or maybe jayce, then sure I'm down

Or Teemo. Everyone underestimates the furry bastard.

I think the champion isn't really that relevant ... Imagine yourself being fed and your team surrendering the game. :/