Batman: The Animated Series (1992)

Heart of Ice - S1-E3

Stupidity: Ferris Boyle tries to cover up his sabotage of Victor Fries' experiment, but he opts to store the incriminating security tape of the event in a filing cabinet instead of simply destroying the footage.

Phaneron

Show generally

Stupidity: In many of the episodes, when Batman is captured by one of his many enemies such as Joker, Two-Face, the Mad Hatter, etc. and restrained, nobody even bothers to pull off his mask to reveal his secret identity.