It was a scene from The Mummy that really got me.

The Mummy is avenging itself on all of those who have entered its tomb. One guy, a little professor or something, is being stalked by the Mummy. He sees him standing outside his kitchen window, etc, and everybody decides the little professor is nuts. We know different, though.
Anyway, they lock the little guy away in a cell with one window covered by bars and a screen. "No one can hear you in here," says the white-coated attendant as he locks the door. "If you need anything, ring the buzzer," and he points to a huge doorbell-like buzzer on the wall. The little guy is actually relieved to be locked in this cell, safe from the clutches of the Mummy. He eases back in his chair...but what do we see in the shadows across the lawn of the asylum? What in God's name is stumbling out of the trees, lurching toward the window? You want to yell Behind you, Little Guy! Turn around! And finally, he does. But what does the numbskull do? Does he push the frigging buzzer that's in plain sight? NO! He beats on the door! "Oh, Please someone!!! Help me I beg you!! AAAAGGGHHH!" The little guy is beating on the door with the chair while the Mummy is ripping the screen off, and everybody in the theater is shouting "Just ring the damn BUZZER!!!!" But of course, he doesn't, and the Mummy bends the bars apart, grabs the guy in his supernatural Mummy death-grip and kills him, then clambers out the window.
Learned a very basic lesson at that early age...Pay attention to the instructions!