Visible crew/equipment: During "Valerie", as Santana resumes singing right after Mike has somersaulted over Brittany, you can see a cameraman filming the girls' group in the bottom left corner of the screen. (00:32:15)
Visible crew/equipment: In "The Power of Madonna", just before Sue drops the Madonna CD onto Figgin's desk, a camera is briefly visible over her right shoulder.
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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