Continuity mistake: When Sam is talking to and kissing Nurse Penny in her office, Nurse Penny's lanyard keeps moving from the left side (on screen) of her name badge to the right side and also sits on top of the badge. (00:43:00 - 00:45:00)
Factual error: They sing Katy Perry's "Roar" before the song was even released. This episode is set in Spring 2013 and the song was released in August.
Answer: The show is purposefully stylized and over the top. It is not designed to be an accurate, realistic representation of American high school. The idea that the glee club is so unpopular other students can literally throw garbage at them with impunity is an over-exaggeration of how glee club is considered "un-cool" compared to things like football. However, there is a second way of looking at it. The audience is simply never shown anyone getting into any trouble for throwing slushies. Just because we don't see it doesn't mean it never happened.
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