I have a similar fantasy on occasion. In mine, the setting is usually a biker event. In a group conversation, someone jokingly mentions enemas, hoping to embarrass more timid members and get a laugh. I off handedly make the remark "Shit, sign me up for that" and we all have a good laugh.
Later on, away from the group one of the ladies who is somewhat soft spoken, starts up a friendly conversation with me. Though she hasn't mentioned it, I can sense that it was the enema comment from earlier that has sparked her interest. We engage in friendly chit chat, circling the conversation and waiting for the proper innuendo that will lead us to the real topic of interest.
Then, without warning, her eyes lock on mine and she asks, "So, you want signed up for a good enema, huh?" I gauge the look on her face and see that she is a little nervous, hoping that her direct approach does not backfire on her. I calmly and sincerely answer - "Oh, without a doubt".
From there the fantasy streams off into arousing conversation about erotic likes and dislikes - will you let me give you - will you give me, etc.. As the day draws to a close we retreat to a hotel room and… you can fill in the blanks however you see fit.
The thing that makes this fantasy different than others I've had, is that the bulk of it ends up playing out as to what the conversation would be like, and excitement of talking low low enough to keep it private amongst a crowd of people who all seem compelled to come up and say hey and give you a bro, hug