I am expecting a lot of Disco Elysium, here...and nothing wrong with that!
A video gaming student organization I was once part of actually had a vote on their favorite sayings. The winner was the evergreen "Perhaps the same said could be said of all religions..." from Castlevania: Symphony of the Night! https://www.youtube.com/watch?v=OMTizJemHO8
Later we had a second voting, which decided on the cult classic Trio the Punch's "BAD CHOICE"! https://youtu.be/rIPtzZHJnkg?t=454
My personal favorite? It's hard to say...but hey, that's what the scientist in Half-Life can comment, word to word! So maybe I'll put forward, said by the aforementioned: "My god, what are doing!?"
Tl;dr: Check title.
Too bad Bungie run out of time. You can tell Halo 3's story was hastily assembled from the bits they had left over from Halo 2's intended climax