I don't think it's a well - known or popular story considering the rather strange and unclear title. There are no common references to such a story that I'm aware of.
I'm not sure specifically what that story is about as the title is rather unclear and a bit odd. It could potentially be about boys wearing Speedos and some sort of incident or activity related to that, but without more context it's hard to say for sure.
I'm not sure specifically what a 'speedo cock story' is. It could potentially be a made - up or very niche story related to someone wearing a Speedo (a brand of swimwear) and perhaps an incident involving a rooster (cock can refer to a male chicken) in a really strange and specific context, but without more information, it's hard to say.
Well, there are many speedo stories. For example, at a beach volleyball tournament, a guy wearing a bright red speedo made an amazing dive to save the ball and became the talk of the beach that day. His confidence in that speedo was inspiring.
I haven't personally heard of a'speedo cock story' before. It might be something very local, personal, or just a very unique term that not many people are familiar with.
Sharing 'cock cum stories' with your sister is extremely inappropriate. Family is a place of love, care and positive interaction. Such vulgar content has no place in family communication. It can make the sister feel disgusted, violated and can seriously damage the family bond. Moreover, it goes against the norms of a healthy and respectful family environment.