I laughed out loud at that point - great line. The script is surprisingly good.
It makes me wonder how much they actually wrote/recorded. 1 of the Dev Commentaries (after reviving GLaDOS) says that playtesters found her a bit too... malevolent initially (after all she's talking to her 'murderer') so they redid it to make her have more of a 'slow burn'. Not just a "**** it that'll do" moment in the slightest.
The parts towards the end where GLaDOS is winding up Wheatley are hilarious too. "This statement is false" "er... true".