Stupidity: The 10,000 Volt ghost wears a diver's suit to insulate himself against the electricity, yet he doesn't cover his hands.
The Ghost that Sacked The Quaterback - S1-E15
Stupidity: It's hard to believe that prior to building a new stadium the owner wouldn't remove all the trophies and memorabilia from the old stadium's sports hall.
Stupidity: The ghosts should've noticed the money they were stealing from the US Mint hadn't got its serial numbers and Treasury seals yet.
A Frightened Hound Meets Demons Underground - S1-E14
Stupidity: The bad guy is dumb enough to stay in the basement of Captain Sally's instead of taking his loot and fleeing.