“We won't be seeing you," Fred told Professor Umbridge, swinging his leg over his broomstick.
"Yeah, don't bother to keep in touch," said George, mounting his own.
Fred looked around at the assembled students, and at the silent, watchful crowd. "If anyone fancies buying a Portable Swamp, as demonstrated upstairs, come to number ninety-three, Diagon Alley — Weasleys' Wizard Wheezes," he said in a loud voice, "Our new premises!"
"Special discounts to Hogwarts students who swear they're going to use our products to get rid of this old bat," added George, pointing at Professor Umbridge.
"STOP THEM!" shrieked Umbridge, but it was too late. As the Inquisitorial Squad closed in, Fred and George kicked off from the floor, shooting fifteen feet into the air, the iron peg swinging dangerously below. Fred looked across the hall at the poltergeist bobbing on his level above the crowd.
"Give her hell from us, Peeves."
And Peeves, who Harry had never seen take an order from a student before, swept his belled hat from his head and sprang to a salute as Fred and George wheeled about to tumultuous applause from the students below and sped out of the open front doors into the glorious sunset.”
- J. K. Rowling, Harry Potter and the Order of the Phoenix
Ahhhh, take that you old hag :D. What's your favourite moment in book five?