I'm left with a couple of questions.
First after I saw the film, I listened to Slate spoiler specials, and the reviewers said that they thought that the naked party scene was a fantasy in one of the characters' minds. Did I miss something? I saw no indication or transition indicating that scene was a fantasy, but was instead part of the reality of the narrative.
Finally, I wonder if the equivalent milkshake scene in the film is in the middle, not the end. Maybe the film should be retitled "The Mastur."