The Ticket - S7-E1
Continuity mistake: This episode (after the library scene that takes place three years later), according to Josh, takes place four days after the National Democratic Convention shown in 6x22. Somehow in that 4 day period Josh's hair has grown considerably and Jed's hair has become much grayer.
Chosen answer: A really annoying innate lack of sense. My friends and family say the same thing all the time, and I'm endlessly trying to correct them. I think people just don't know any better and (ironically) couldn't care less that they're speaking incorrectly.