This quote/statement(When I See a Pretty Girl Walking Down the Street) was said by a serial killer of 1950s by this it show his dual personality. One personality shows he nice person just like other who wants to be in love. Other statement tells that he is a psychopath who wants to murder beautiful girls and preserve their faces at his home on stick just like when a person hunts a animal hang it on the wall.
This quote was also used in American Psycho Movie:
Bateman: Do you know what Ed Gein said about women?
Van Patten: Ed Gein? Maitre d’ at Canal Bar?
Bateman: No, serial killer, Wisconsin in the fifties.
McDermott: So what did Ed say?
Bateman: When I see a pretty girl walking down the street I think two things. One part of me wants to take her out and talk to her and be real nice and sweet and treat her right.
McDermott: And what did the other part think?
Bateman: What her head would look like on a stick.