The following is a liste of some of their greatest moments. Most of these are from the books. However, these first two are from the DH1movie. Enjoy!
Moody: Fair warning: it tastes like goblin piss.
One twin: How do toi know what that tastes like? *sees Moody's glare* Just trying to ease the tension.
Both: *after transformation* Wow. We're identical.
Ok. Here we go with citations from the books. Don't forget to comment. Also, add any I may have missed.
"Fred, toi next," the plump woman said.
"I'm not Fred, I'm George," a dit the boy. "Honestly woman, toi call yourself our mother? Can't toi tell I'm George?"
"Sorry, George, dear."
"Only joking, I am Fred," a dit the boy, and off he went.
"Blimey," a dit the other twin. "Are you--?"
"He is," a dit the first twin. "Aren't you?" he added to Harry.
"What?" a dit Harry.
"Harry Potter," chorused the twins.
"Aaah, has ickle Ronnie got somefink on his nosie?" a dit one of the twins.
"Hang on, I think I remember him saying something about it," a dit the other twin. "Once--"
"Blown up a toilet? We've never blown up a toilet."
"Great idea, though, thanks, Mom."
"Never mind that, do toi think he remembers what You-Know-Who looks like?"
"We'll send toi a Hogwarts toilet seat."
"We got Potter! We got Potter!"
"You must be good, Harry, Wood was almost skipping when he told us."