I won't list all of them now, but since XIII is fresh in my mind, I'm gonna go with chapters 9 and 10. Through the game was bad before, this is where my patience with the hallway ended. Especially since right after that we get Gran Pulse which is decent enough, if way too little too late and you still get limited access to the Crystarium, wtf. In general XIII is probably my least favorite moment in the series.