I don't know. People are weird creatures. A friend of mine's ex-wife was violently raped by a guy while his friend watched and laughed when she was in high school when she was still a virgin. He later told me she liked being choked, smacked, etc. when they had sex together. I thought it was weird at the time, but have since found out quite a few women who have had traumatic experiences like that develop a kink for that type of thing in consensual encounters. Summer definitely seemed more into Max's nastiness in following scenes.

Or maybe Max just knows more about charming(some might say manipulating) women into doing things they normally wouldn't than the average joe.