Revealing mistake: At the New Years Eve Party, Cindy gets drunk and starts looking for a bedroom to lay down in. As she opens bedroom doors, she interrupts couples making out. When she interrupts one couple there is a shoe thrown at the door, supposedly from inside the room. If you look closely you can see that the shoe is actually thrown from behind Cindy's head outside the bedroom door.
Revealing mistake: In each of the school lunch scenes, you can observe that all the food items and soda cans are glued to the trays by the way the students are carelessly carrying the trays around.
Revealing mistake: Near the end of the movie, Ronald wakes up Cindy by running his lawn mower outside her house; both Cindy's clock and Cindy herself say it's 6 a.m. But the sun is completely high overhead - no shadows - which indicates it's actually much later than that.