Stupidity: After Cory and Shawn fish Mr. Feeny's watch from the septic tank, he suggests they jump into the lake to clean off. Cory protests, reasoning that it's only 20° outside, to which Feeny dismissively tells them to take a sweater. They then reluctantly abide. Someone of Feeny's education should know better than to allow them to jump into a freezing cold lake. They could both get hypothermia, and they're all currently isolated in the Pocono Mountains with no nearby medical facilities.
Stupidity: When Eric, dressed in drag, tearfully sits down next to Topanga, she asks him if they know each other because she doesn't realise it is him. Topanga's known Eric practically her entire life, and she is one of the smarter characters on the show. Given that Mr. Feeny instantly recognized that Eric and Jack were dressed up as women, Topanga should have recognized it immediately as well. (00:10:40)
Stupidity: This episode shows the school's faculty time-clock to be in a common area of the school. Placing a time-clock in such an area would be extremely foolish, as any disgruntled or prankster student could easily mess with a faculty member's timecard. Not to mention the episode shows Janitor Bud bribing a student to clock him out long after he has left for the day.