What should I do if a girl in a black dress playfully touched the genitals of a naked young man on the beach?

In a situation like this, it's vital to assess the context and the reactions of those involved. If both individuals seem to be consenting and are comfortable, it may just be a playful interaction. However, if it seems to be non-consensual or makes anyone uncomfortable, it's important to intervene appropriately. Here are some steps you could take:

**Assess the Situation**: Observe the body language and reactions of both individuals. Are they laughing and enjoying themselves, or does it seem forced or uncomfortable for one of them?

**Respect Boundaries**: If either person seems uncomfortable, it’s important to intervene or distract them to create distance from the situation.

**Intervene if Necessary**: If you believe it's inappropriate or non-consensual, approach the situation calmly and respectfully. You can make a light-hearted comment to ease any tension or gently steer them away from each other.

**Seek Help**: If the situation escalates or if you feel it could lead to harm, seek assistance from authorities or lifeguards nearby.

**Create a Safe Environment**: Encourage a respectful atmosphere where everyone can feel safe and comfortable.

Overall, the key is to ensure that everyone involved feels safe and respected.