1) Playing Imperial March when a professor walks into a room is not appropriate. (We know it's you Fred and George, we just can't prove it)
Professor McGonagall was flustered, she hated being late for anything. When she swept into the classroom, her eyes instantly fell on the Weasley twins, as they looked like they were up to something.
She marched up to her desk and pulled out her wand. Then it started. 'It' being the muggle theme tune from that sci-fi movie.
Her eye twitched minutely, then she lost it. She cast a silencing charm, stopping the music, just as she was about to put the entire class in detention, it started again.
The class began laughing at the professors shocked expression, before she screamed at them.
"One hundred points from each of you, and a weeks detention!"
The class was silent, and the music stopped. McGonagall started the lesson.
She knew who it was, but couldn't prove it.