Three letters and a number: MGS4. Yeah, the story is amazing, and most of the dialogue is great (or at least decent), but there are a few lines that stand out as possibly the most horrible lines I've ever heard in a game.
Raiden: "It even rained on my birthday."
Old Snake: "You were the lightning in that storm!"
Booooooooo.
Also:
Naomi Campbell: "Snake, if you won't be a prisoner to fate, then go... Fulfill your destiny."
<url=http://0uterheaven.files.wordpress.com/2009/04/mini_game_004_by_goldsickle.jpg>Contradiction does not compute.
Say what you want about the translation process screwing up the dialogue, those are still horrible lines.