Most annoying character, ever.

[Niolani]

I was about to say Navi but I think Ciela, from Phantom Hourglass, is far more annoying than her. This picture explain a lot.

[MadballChibcha]

Natalya in GoldenEye 007 made me cringe at the screen sometimes. She´s not "actively" annoying like others posted, but she´s really nosy, meddling constantly within massive gunfights with a total disregard for herself, and ONE accidental shot from your gun and mission crapped.