This could be about a mother teaching her son appropriate behavior in the context of storytelling. For example, she might be guiding him not to include inappropriate or vulgar content in the stories he tells.
Sharing or seeking such sexually explicit stories is inappropriate and not suitable for public discussion. We should focus on positive, healthy and respectful topics.
The phrase can be a turning point in the plot. It might make the other character stop and think about the relationship and the potential consequences. It also adds an element of power dynamics as one character is setting a boundary.
I'm not sure if there is such a specific fanfic available. Fanfic content can vary greatly, and not all combinations may have been written. You might try searching on specialized fanfic websites.
I'm not entirely sure what you specifically mean by 'cum for mom story'. It could potentially be a story about a son or daughter achieving something great for their mom, like getting a high - grade scholarship to make her proud.
Rather than exploring this improper - sounding story, we can turn our attention to heartwarming family - friendly stories that promote positive values.