Trivia: When Donnie is about to enter the car with Gretchen near the end of the film, he clutches at his stomach as if in pain, and we see Frank touch his eye after Donnie dies. Both these moments foreshadow pain: a deleted scene of Donnie's death shows a pole impaling his stomach right where he clutched it. And Donnie shoots Frank in the eye.
Trivia: The time when the world is supposed to end is 28 days, 6 hours, 42 minutes, and 12 seconds. 28+6+42+12=88. The year the film takes place is 1988.
Trivia: In the "Cunning Visions" infomercial, Jim Cunningham (the man arrested for having kiddie porn) grabs the young boy actors behind.
Trivia: In the scene when the English Teacher is packing to leave her job, and Donnie asks about the meaning of 'Cellar Door' written on the board. She responds 'A famous Linguist once found those were the 2 most beautiful words in the English Language'. The Linguist she was referring to: J.R.R. Tolkien, (author of 'The Lord of The Rings' trilogy).
Trivia: Some of the people in Jim Cunningham's video make cameo appearances at Donnie's school. The little boy on the video is the same kid that asked "how can I learn to fight" at the assembly in the auditorium. Also, the older girl in the video is the same girl who shows the newspaper with Jim Cunningham's arrest to Miss Farmer in the High School's main office. Their presence and/or placement at the school seems to indicate that Jim Cunningham's entire "Q + A" seminar at the school was staged, including the questions to be asked of him. This would also prove Donnie right about Jim Cunningham being a fake, only pretending to help people, as well as explaining his rapid success which is evidenced by his large home.