I just saw the movie this past week-I know, I'm lame.
But the movie is fresh in my mind, and I could totally picture something like this coming from Dignam. And it fits their relationship that Billy would both appreciate it and let Dignam know he had the wrong words!
I really wish they had scenes in the movie like this between them!
I enjoyed reading this. I hope you write more Departed fic with the two of them.