This is apparent in the shots of nudity when Charlie sleeps with his prostitute girlfriend Clarissa, and with some of the general sexual conversation about virgins and breasts and so forth.
Also, there is some degree of complexity in Charlie's character, which is partly like art films, but he does not in fact have any of the contradictory traits common to art cinema. One may be tempted to say he is timid at times, and bold at other times, and these indeed make for contradictory personality. However, there is commonality in all of the times that he acts boldly. When he fights and kills Plyne, when he is having sex with Clarissa (she screams "and to think people call you timid!aE), and in the flashback when he is a virtuoso pianist (having his picture taken by the media and so forth) he certainly appears to be bold. However, all these times are the times when he has a woman, or a girlfriend in his life. Without a girlfriend, he becomes very timid and afraid. This relationship makes it very easy to understand Charlie