Take the Lead (2006)

Continuity mistake: When Mr. Dulaine forces Rock and LaRhette to dance the waltz together, he takes off his necktie and blindfolds LaRhette with it. Throughout the scene the blindfold is different nearly every time the camera angle changes - the "tail" created by the wide end of the tie gets longer and shorter, the knot alternately loosens and tightens and moves from side to side across the back of her head, and the whole thing slides up and down her nose. It's so distracting I spent the whole scene watching to see how it was going to move next.

Pierre Dulaine: I want to teach your kids to dance.
Principal Augustine James: If theres' one thing they can do, it's dance.
Pierre Dulaine: Ballroom dance? Waltz, the foxtrot?
Principal Augustine James: Ok, where's the camera? Because if you're saying that you want to teach my kids the foxtrot I have to be on TV.