>>15242299"Carrie" was a movie made in 1976 about a weird girl going through puberty. But was also a demon child. The school bullies/assholes elect her as prom queen then dump pigs blood all over her on stage (as a reference to her not knowing what a period was when she started hers in gym class. The girl's threw tampons at her, not that it's relevant here)
The pigs blood caused her to flip. She magically seals the doors to the gym where the prom was taking place and burns everyone inside.
The reference would have been better if the Maniac also had a Grumpig but I doubt the japs were in on the joke.