I'm a really big fan of "Fight Club" and I thought I knew pretty much everything about it.  I've read the book, know all about the little hidden details of the movie and I thought i had seen all the deleted scenes.  I don't know how, but I missed one scene, the one with Brad Pitt and Edward Norton singing about penis.

I guess this isn't so much a deleted scene, but more so footage of Edward Norton and Brad Pitt goofing around.  I'm sure they had a pretty strong bromance going on during filming.  The scene in Fight Club where they are hitting golf balls in the street stems from that bromance.  Pitt and Norton were bored during a late night shoot and the director saw them trying to hit the catering truck with golf balls.  He rolled cameras and liked the footage so much he wrote it into the script.