Slaughter High (1986)

Plot hole: The school is supposed to be rundown and closed after ten years yet Marty somehow manages to get in, rig up all his traps (including the acid through the bath pipes), and setup the reunion supplies without the caretaker ever catching on to anything that's going on. It also begs the question if the caretaker was there the whole time until he was killed how did he not notice the other students waiting outside for several hours or their cars to ask what they were doing while outside?

jbrbbt

Plot hole: In the opening scene, the bullies all go into the girls' toilets with loads of camera equipment, including high tech ones used for proper films and boom mics. This equipment is way too expensive (even more so in the 80s when the film is set) for any high school kid to have.

swordfish

Plot hole: When the bullies take revenge on Marty, they doctor the chemicals he is preparing so that they explode. The bullies were punished some time in the afternoon, judging by the sun in the very first shot. Their detention is at 4:30 in the afternoon. Somehow, they manage to acquire the necessary chemicals for the explosion within a couple of hours, even though they are stuck at school. In addition to this, they have no way of knowing what chemicals Marty is preparing, so even if they were able to get chemicals, they would not know which ones to get to destroy his experiment.

swordfish