Dave is disgusted, insisting that Sheila wouldn't like it if someone treated HER like that. However, Sheila says she wouldn't CARE.
That's when Dave decides to take her up on that challenge by bullying and humiliating her. He does everything from making fun of her, to pulling her hair, to even giving her a wedgie. But Sheila refuses to admit that ANY of the treatment is bothering her... even once it becomes clear that they're BOTH secretly getting turned on by the twisted event.