Ecael wrote...
Kian Louros: I would be glad to give you our employee discount if you could do that for us.
[Neutral Interrupt]
Shepard: I'm Commander Shepard, and this is a store on the Citadel.
Kian Louros: ...
I thought of that when reading page 1, but you beat me to it by several months, so I don't have to do it. Well said

A couple of others I thought of (the first couple of scenes turned out to be covered, but differently):
Joker: What's the order, Commander? Come in now to save the Ascension or hold back?
[Neutral Interrupt]
Shepard: How about just sending half of them?
*All ships except the Normandy are destroyed by the end of the battle*
Shepard: I should go
-----
Niftu Cal: I am a biotic god! I think things, and they happen! Fear me lesser creatures, for I am biotics made flesh!
[Neutral Interrupt]
Shepard: I should go.
Niftu Cal: No! Wasea is mine to destroy! If I must end you first, so be it!
*Biotic spark zaps Shepard's nose*
[Neutral Interrupt]
Shepard: I should go.
Niftu Cal: B-b-but... wait! *runs after Shepard, trips, and knocks himself out*
----
*Kaidan shows up at the end of Horizon mission*
[Neutral Interrupt]
Shepard: I should go
Kaidan: But... we haven't talked in 2 years!
[Neutral Interrupt]
Shepard: Actually you're only here because it's the default for a non-imported female character. To me you're just the former squad member who apparently didn't die, so I don't really care what you have to say.
Kaidan: huh?
[Renegade Interrupt]
*Shepard Puuunch*
----
*Jack and Miranda are in the middle of their big argument*
[Neutral Interrupt]
Shepard: I should go. Try not to kill each other until I get back with the camera.
*Jack and Miranda team up, Shep awakens the next day to Doc Chawkas' expression of disapproval, and you lose both loyalties. Joker thanks you for the footage.*