When I first started watching Supernatural, I kept thinking Sam was Dean. It took me a full season to really grasp who was who. Then I remembered that Jared played Dean on Gilmore Girls. And it all made sense.
That is my favorite gag reel moment! I swear, they must put a little bit of crack or something in their food on set and that's what causes them to be so silly. If you don't believe, just watch one of the gag reels. It doesn't matter which season, just watch one of them.