Continuity mistake: Gretchen starts talking to that man who doesn't talk, but later when Mikey is singing for the first time, you see that man booing him, then a minute later Gretchen is still talking to him.
Some Friend - S4-E44
Plot hole: They say in this episode that Menlo was always an organized freak. But in "Principal for a Day" it turns out that he was a hyper-major kid until he started working in the school office.