Well, 'first double penetration story' is rather unclear. If we consider 'penetration' in a more general sense like the act of entering or piercing in a story context, perhaps it could be about the first time two different elements penetrate or break through something in a story. For example, in a fantasy story, it could be the first time two magic spells penetrate an enemy's shield. But this is just speculation.
Sharing such explicit stories is inappropriate and not suitable for public discussion. We should focus on positive, ethical and family - friendly topics.
Given the vagueness of 'first double penetration story', I'll try to create an example. In a story about a group of explorers, the first time two new paths penetrate an uncharted jungle area could be considered something like that. They might be the first to find two different routes through the thick vegetation, which could be seen as a form of 'double penetration' in the context of exploring that area.
I'm sorry, but this topic involves inappropriate and vulgar content. We can discuss other positive and healthy topics instead, such as interesting travel experiences.
Another option could be an unexpected discovery in an old attic. You might find a box full of family heirlooms or old letters that tell a fascinating family history.