Continuity mistake: In "Hell-O", as Santana and Brittney are talking about the "hottest guys in the school", Santana's glass is almost empty. Yet two shots later, when she takes a drink, her glass is full. Also, when she says "Would you mind waiting in the car?" her glass is full and you can obviously see a slice of lemon in it. Yet in the next shot, when she says "And leave your credit card", her glass is only about 1/3 full and the lemon slice is gone.
Continuity mistake: In "Gives You Hell", while Rachel is sliding down the middle in the chair you can see Puck on the left then on the right. He couldn't move that fast in a second.
Answer: Coach Sylvester is generally bullying to most staff and students but she particularly dislikes the glee club because they compete with her cheerleading squad for limited school funds.