Lilarcor: "Can we go kill something now?"
Keldorn: "Aye, as you wish."
Jan (when attacking Beholders): "Beware! Your knees are mine!"
I think the most perfect, and at the same time most improbable, party interjection was when doing Xzar's quest. We'd just delivered the bird to him, he Polymorphed it back, and then suddenly Jan piped up, "Minsc! Look out! Behind you!" freezing the screen
just as Lucette had her weapon raised, poised to strike.
It's my own damn fault I forgot to take a screenshot.