User blog comment:JakePT/Arrival has Arrived/@comment-730941-20110330133813/@comment-730941-20110330140820

It was part of the "Hackett and Cerberus" dialogue choice - after the bit where Hackett says something to the effect of "at least Cerberus are looking at the state of the galaxy".

The line, according to YouTube footage, was (in response to Shepard's "I didn't expect to see you aboard a Cerberus vessel" question):

"Besides. I'm not so sure this is a Cerberus vessel anymore. Right?"

I'm thinking it had to do with the Collector base decision, but it could equally be the dialogue choices with the Illusive Man.