This whole interchange:
Dr. Hawkins: Kurt? Kurt? Can you hear me my boy?
Max: Doctor, we're not getting through to him.
Dr. Hawkins: Oh, nonsense. He's always been quite reasonable. Something is just blocking the signal. It's that ship!
Max: Hmm. We could destroy their power supply so they stop jamming us.
Dr. Hawkins: No, no, no, I've got a better plan. You should destroy their power supply so they stop jamming us.
Max: Grrr.
Dr. Hawkins: Heel. Good Doggie! Now, go straddle a torpedo while I figure out how to aim. I love surplus!
MDK 2, still one of BioWare's best games.
And of course Portal. Where to even begin, so many of the good one's have been mentioned but lines where GLaDOS constantly marginalizes devastating consequences are particularly good.
"The Aperture Science Center promises to always offer safe testing environments. In dangerous testing environments, the Aperture Science Center promises to offer helpful advice. For instance, the floor here will kill you. Try to avoid it."
"While safety is one of many Enrichment Center goals, the Aperture Science High-Energy Pellet, seen to the left of the chamber, can and has caused permanent disabilities, such as vaporization. Please be careful."
But I think one of my all time favorites is the big 'reason you suck' rant she gives Chell at the end:
"I'd just like to point out that you were given every opportunity to succeed. There was even going to be a party for you. A big party that all your friends were invited to. I invited your best friend the Companion Cube. Of course, he couldn't come because you murdered him. All your other friends couldn't come either because you don't have any other friends. Because of how unlikable you are. It says so here in your personnel file: Unlikable. Liked by no one. A bitter, unlikable loner whose passing shall not be mourned. 'Shall not be mourned.' That's exactly what it says. Very formal. Very official. It also says you were adopted. So that's funny, too."
You could made a thread like this solely based around that game.