In the story "Where Are You Going, Where Have You Been" by Joyce Carol Oates, Connie, the teenage protagonist, is in trouble because she is so unsure of herself and her identity. The man who comes to her door when she is alone uses manipulation and disguise to lure her to his car. Because she is used to controlling boys by flirting, she doesn't realize she is in danger until it is too late. The "grin or smile" is the opposite of what Connie wants to do, but is an outright demonstration of control by the dangerous Arnold Friend who tells Connie what she must do. He knows he has won the struggle for control of Connie while she realizes that she has lost her identity and perhaps her life in the hands of this man ironically named Friend. So the "grin or smile" is ironic in the sense that it is used to show control, not friendliness. Without the ability to detect reality underneath the disguise, Connie has become a victim of her own lack of strong self and the manipulation of a man who victimizes others.
With Connie, the smile is used in two ways.
Everything about her had two sides to it, one for home and one for anywhere that was not home: her walk that could be childlike and bobbing, or languid enough to make anyone think she was hearing music in her head, her mouth which was pale and smirking most of the time, but bright and pink on these evenings out, her laugh which was cynical and drawling at home - "Ha, ha, very funny" - but high-pitched and nervous anywhere else, like the jingling of the charms on her bracelet.
This is a dark transition, being situated or loosely based upon the historical account of a man in Tuscon, Arizona who lured and killed several girls in the 1960s. The story itself is a loss of innocence, a transition from young woman into adulthood. At such a bifurcation, Connie knows only two ways to be: at home, she is a cynic and away from home she is a typical teenage flirt. In both identities, her smile is either sarcastic or a performance via flirtation with other boys.
Arnold Friend's smile is also contrived. It is a performance. His smile is part of his incantation, the spells and flattery he uses to lure girls into his car.
Connie is forced to depart from her home and "away from home" identities as she finds herself in a more serious role of being a sexual object. Her fake smiles will not get her out of this situation. Her fear of the situation leads to a breakdown when she rushes for and screams into the phone for her mother. She then becomes like a passive object (objectified) perhaps as a way of coping. "She was hollow with what had been fear, but what was now just an emptiness." As this may indicate a regression (crying for her mother) or a progression (agreeing to go so Arnold would not harm her family), in either case, her smile is gone.
Arnold's smile is just as contrived but obviously more sinister. Connie recognizes that his smile, his whole performance and appearance, were all fake. In fact, his smile disappears when she questions his age.
His smile faded. 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.
By the end, Connie realizes that her cynicism at home and her flirtation away from home were manifestations of her adolescent identity crisis. And she realizes that Arnold is more like a predator than a flirt himself.
Aside from its general, genuine purpose as an involuntary gesture of happiness, the smile in this story is a tool used to perform. Connie uses it to flirt. But the gesture of the smile in this story is most often used in describing Arnold's attempts to manipulate Connie. It is, in his case, a sinister mask he uses to trick the much younger, more innocent girl.