Prior to the most drawn out demonic possession ever filmed (I'm only guessing here), there was a scene in the basement of the house that had us cracking up and making up our own dialogue. The eldest son is alone in the house and he had gone to the cellar to get a gun because he heard some noises that could have been an intruder.
All of a sudden he hears whispering voices from behind some hidden panel in the cellar. He yells out "Who's there? I can hear you!". That's the point when we started our own MST3K-ish dialogue, imagining what the mysterious voices in the cellar were really talking about:
Satan: You idiots! He can hear us.
Beelzebub: It wasn't me, it was Azazel!
Azazel: NOT! Satan, he's always blaming me!
Satan: Enough with the squabbling! I've had it with you two!
Mephistopheles: I WANT TO POSSESS HIS SOUL!!!
Satan: Shhh...inside voices, Mephistopheles. Inside voices.
Mephistopheles: I WANT TO POSSESS HIS SOUL!!!
Satan: (to himself) I can't believe I'm stuck in here with these guys.
Azazel: Satan! Beelzebub is touching me!
Satan: (slaps his forehead) Crap!
The movie just got better and better from there. Spousal abuse, child abuse, and incest. Yes...the creepiest incest scene ever filmed (I'm only guessing here). The brother visits his sister in her bedroom one night. He asks her to play the model/photographer game, and that's fine. I mean, who hasn't played that game with his sister every once in a while. But then he asks her to take off her nightgown. Her response? "OK, but only for a minute!"
You can imagine where the evening goes from there.

You're imagining it...aren't you? Sickos!