It would be easy to brand Patrick Bateman, the titular protagonist in Bret Easton Ellis’ 1991 novel “American Psycho,” as a less-than-admirable guy. The coke-sniffing Wall Street banker is narcissistic, misogynistic and — yes — sadistically murderous. And yet for the image-conscious, Bateman — played by Christian Bale in the 2000 film and, starting this week, by Benjamin Walker in a new Broadway musical of the same name — has become a kind of icon. And not just on Halloween. Google it. The Internet is awash in prescriptive guides: “How To Dress Like American Psycho,” proposed Complex in 2010; “Beauty Secrets From 5 Real-Life Patrick Batemans,” offered New York magazine’s The Cut in 2014. Men’s shopping giant Mr. Porter has even teamed up with “American Psycho: The Musical” to outfit Walker and other male cast members in pieces that will also be available for purchase online. See more at New York Post.