Continuity mistake: Josh is wishing Donna a Happy Thanksgiving - he is eating something out of his hand and has a blue book tucked under his arm, which flips from front to back from one shot to the next. When he starts talking to the Trekkie, it flips back again.
Continuity mistake: When Josh is recapping his conversation with Jack to Donna, as he is walking towards the coffee pot he his putting a pen in his shirt pocket. When they turn to walk back to his office the pen has disappeared. (00:24:50 - 00:25:50)
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.