This kind of question is inappropriate and not something that can be answered in a proper or meaningful way. We should focus on positive and respectful topics.
Well, if we think of 'black cock' as a drink (like black coffee) and'sissy' as a person who is a bit timid. The story could be that the sissy has never tried strong coffee (the black cock) before. One day, out of curiosity, he takes a sip and it gives him a new energy. And this experience starts a journey of him becoming more adventurous.
I'm not sure specifically what this 'black cock hypnosis for sissy story' is about as it seems rather unusual and not a common, well - known concept. It could potentially be some sort of fictional or niche - themed story within a very specific community or someone's creative but rather odd idea.
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.