There are so many of them but here are a few
"Romancin´ is varrae important ye ken. Basically it´s a way the boy can get close to the girl wi´out her attackin´him and scratchin´his eyes oot."
Terry Pratchett, Wintersmith
"The creator had a lot of remarkably good ideas when he put the world together but making it understandable hadn´t been one of them"
Terry Pratchett, I think it is from The colour of magic
"But here is some advice, boy. Don´t out your trust in revolutions. They always come around again. That´s why they are called revolutions. People die, and nothing changes" Terry Pratchett, Night Watch
"Oh, please sue the University! We´ve got a pond full of people who tried to sue the University...! Going Postal