Arnold Friend transitioned from a passerby on a midsummer night, whose face Connie couldn't remember for the life of her, to a guy whose face she would never be fortunate enough to forget.
This transformation was what was so appealing to me about Joyce Carol Oates' character. As his advances toward her progressed from awkward to creepy to frightening, Connie began to further understand who Arnold Friend was. As Connie continued to deny his requests, Arnold's smile faded, and in doing so, "She could see then that he wasn't a kid, he was much older - thirty, maybe more. At this knowledge her heart began to pound faster." Oates further goes on to say, "She watched this smile come, awkward as if he were smiling from inside a mask. His whole face was a mask."
What Joyce Carol Oates did the best in this short story, at least from my perspective, was using a character as disturbing as Arnold Friend to keep both Connie and the reader interested in what he was saying enough to fight the growing urge to ignore him. She did this successfully with various forms of persuasion ranging from flirtation to threats. He initially was saying how he was infatuated with her and how beautiful she was (Connie knew she was beautiful, but it never got old hearing it) and by the end he was instilling in her a helplessness, explaining to her that there was nothing she could do to get away from him, and she knew it, so she might as well do as he said. Just as Arnold Friend transformed, so did the story itself - from lighthearted to essentially scary. Scary stories are more fun to read though.