I see Nolan giving us some fanservice with that Batbooty
During production, Christian Bale followed the morning routine that his character Patrick Bateman describes toward the beginning of the film.
Two scenes featured unexpected improvisation by Christian Bale. When Bateman is jumping rope, he starts to skip and cross his jump rope as a schoolgirl would. Bale surprised director Mary Harron even more by starting to dance as Bateman was preparing to kill Paul Allen (Jared Leto). That time, she says in interviews and the commentary, she collapsed with laughter.