The Indians in the Lobby - S3-E8
Factual error: When President Bartlet is on the phone with the butterball hotline, he claims to be from Fargo, ND. Charlie tells him the zipcode of Fargo is 50504. Fargo has 13 zip codes assigned to it. None of them are 50504. They are all beteeen 58102 and 58126. (00:28:05)
The Indians in the Lobby - S3-E8
Continuity mistake: When Josh is drinking water from a bottle he starts screwing the lid back on as he moves it down towards his desk. In the very next shot, however, not only is the bottle suddenly on the desk without Josh's hands anywhere near it, it also doesn't have its lid on. (00:10:05)
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.