Deliberate mistake: In the shot near the end of the film where Donnie grabs the keys for the station wagon, you can see a Blockbuster Video member card in a cup. That card design wasn't used until the mid to late 1990's. This movie is set in 1988. Deliberate as it's a product placement, but still wrong. (01:37:10)
Deliberate mistake: Frequently during the movie, British surgeons are referred to as "Doctor". In Britain, surgeons are always referred to as "Mister"; this is a hold-over from the surgeon's non-medical past (barbers, etc). This would likely be confusing to American audiences.