There was a scene in one episode that was only aired once, in which Stewie tries to board a plane with a backpack full of knives, guns and grenades. When he walks through the metal detector, he does a little dance to distract the guards and the people that monitor the metal detectors, and as he is walking to his plane he says to himself:
"Let's hope Osama Bin Laden doesn't know show tunes." - The Weird thing is, This episode was made before 9-11.
I believe it was episode 20: Road to Road Island, and it aired on May-30th-2000.