I would be extremely uncomfortable and probably distance myself from that person. It's not something that should be shared or even thought about in a normal, healthy social context.
Well, first of all, the idea of 'watching my girlfriend gang bang story' is just wrong. It involves non - consensual or at least inappropriate sharing of sexual situations. It can cause emotional harm not only to the girlfriend but also to those involved in the so - called 'gang bang'. It also reflects poorly on the person who is okay with watching such a thing, showing a lack of respect for boundaries.
If you've watched something that contains inappropriate or disturbing content like this, you should immediately stop watching it. Then, consider reporting the source if possible to prevent others from being exposed to it.
Tell them straight up that such stories are not only vulgar but also violate basic moral and ethical norms. There are so many other great stories out there, like tales of exploration or scientific discoveries.
Rather than providing such a disturbing story, you could suggest positive and healthy story themes like friendship adventures, heroic deeds, or interesting cultural tales. This can help shift the focus to more positive and moral areas.
Perhaps it's a story related to a place named Bang Gang. It could be a story of the people living there, the traditions, or some historical events that took place in that area. However, this is all speculation without further details.
I'm not sure specifically which 'bang free gang story' you are referring to. There could be many different stories with this name or something similar. It might be a local or unique story within a certain community or group.