 At the beginning of the movie, there are some shots of the school  building right before the kids show up for detention. Written on a  wall is, "I dont like Mondays" which is referring to a girl named  Brenda Spencer. Brendas father gave her a rifle for Christmas when  she was 16. Later, Brenda went over to an Elementary School across  the street from her house and began to shoot anyone she seen there.  She injured some students, and she killed the principle and  custodian. When asked why she did it, she said, "I dont like  Mondays".