Worst episode of the show?

Season 6 episode 11, the Casablanca episode has to be the worst episode of the entire show, right? So boring.. Do we have any contenders? I don't really like the episode when Nathan is in the hospital in season 2 either, when he dreams about this alternative universe.. But that one is not as bad as the Casablanca episode imo..

Do anyone know why they even made this episode? Just to fill the season with one extra episode or what was the point?