There is no evidence to suggest that such activities occur in a gym environment. Gyms have rules and ethics in place to maintain a proper and respectful atmosphere for all members. This kind of description violates the basic norms of a public fitness place.
In such stories, you might find themes of taboo exploration and the challenge of societal norms. But keep in mind that the content can be highly provocative and not everyone's cup of tea.
The term 'big cock wife' in a sexual context is not suitable for public discussion. However, if you mean it in a non - sexual, perhaps a misnomer or a made - up phrase in a non - vulgar sense, there are no such pre - made stories. We should stay away from vulgar and inappropriate expressions.