Most Helpful Girl
That could be basically anything. American Psycho is the first thing that came to mind though.
Most Helpful Guy
There are a lot of psychological thrillers and horror films where a main character plays a psychopath. The first thought that came into my mind is Jack Torrance running around with an ax in the 1980 movie, "The Shining"! Any idea what the character looks like that you're referring to?