FIRST OF ALL: If you are going to say something insulting people, why bother answering the question? Take you insults somewhere else.
Have it be a costume party and ask people to come dressed as their favorite character. The winner of the costume contest gets a prize(such as a twilight T-shirt, poster, book, etc.)
I like the guy above me's idea of having fruit punch, or something red to look like blood. You could also have berry cobbler, since that was Bella's favorite dessert.
Decorate the room with cardboard backdrops such as the orange truck Bella drives, the baseball field, the forest, the school, etc
Hand out body glitter so that people can make their skin glow like when the vampires step into the sunlight
Vote on who can do the best impression of Jasper's face, Edward's face, etc.
You could have a Trivia/Jeopardy game. Divide people into four teams. Then Ask questions related to the movie/book, worth points (100, 200, etc.)
Play Charades. Have people act out scenes from the movie (that they drew from a hat) while the other people try to guess which scene it is.