Twisted Nerve (1968)

"Cleaver. Cleaver. Chop. Chop. First the mom and then the pop. Then we'll get the pretty girl. We'll get her right between the curl."

Martin Durnley is a young man with an infantilizing mother, resentful stepfather and an institutionalized brother with Down's syndrome. To cope, he retreats into an alternate child personality he calls Georgie. After being caught during a theft attempt at a department store, he befriends a female customer who is sympathetic to him, but his friendship soon turns into obsession.