Why in the book "diary of a swimmer" a naked young man asked a girl on the beach to touch his male genitals? And why did she agree to touch?

In the book "Diary of a Swimmer," the scene you're referring to likely explores themes of vulnerability, exploration, and the complexity of human relationships and sexuality. Such moments are often crafted to provoke thought about consent, power dynamics, or the innocence of youth. Without knowing the specific context of the story or the characters' backgrounds, it's essential to approach these topics with sensitivity. Characters may act out of curiosity, peer pressure, or an exploration of boundaries, and their motivations can significantly vary based on their personal experiences and the narrative's context. If you would like a more detailed analysis or a discussion of the book's themes and character motivations, please provide more context or specific passages, and I'd be glad to help!