I didn’t think I would like this (party based on the author, Bret Easton Ellis) but it is now one of my favorite in the dark comedy genre. I think it helps that the screenplay and the direction were by women. Christian Bale is brilliantly at being unhinged just under the surface.
I have included a clip of a Charlie Rose interview with Harmon, Bale and Ellis, to clarify the intentions of the filmmakers. How they explain it is basically how I took it without knowing their intentions.