I was watching Cronenberg's The Fly the other day and there was a real shitter of a scene I'd totally forgotten about.
Gena Davis' character returns to her apartment in the middle of the day and goes to the bathroom to find her shower running. She whips back the curtain to find... dum dum dum!... a male friend of hers who just happened to stop by and let himself in for a quick wash. It really was utter horseshit, and existed only to create a bit of a scare in an otherwise action free scene.
Even the dialogue was awful:
"What's the problem? I was in the neighborhood and was just feeling a bit... scummy."
Can anyone else think of terrible scenes in otherwise perfectly good movies?