Nancy Allen claims she never realized her character in Carrie was going to be so evil until she saw the finished film. She thought she and John Travolta were playing such self-centered, bickering morons that they were there for comic relief.
Piper Laurie also thought the character of Margaret White was so over the top that the film had to be a comedy.
Read more fun facts at IMDB Trivia: Carrie (1976).
The Devil's Muse 