I use this line from the book a lot. I'm not sure if it's in the movie. Anyway, it's when Clemanza asks young Vito if he wanted to know why he wanted him to hide the guns and Vito says,'I'm not interested in things that don't concern me.'
I use that a lot when someone is telling me gossip about someone else. And I often use the 'Bigger Than U.S. Steel' line.