So, I thought I'd get my sea legs before suggesting this, but I figure since the idea is crystallizing a bit I might as well post it and see if I get bites.
Poison Ivy and Harley Quinn have teamed up to capture Batman, leading him to a loft in the ritzier part of Gotham city and leading him to believe he only had Harley to deal with. Caught a bit off guard and unprepared, Batman finds she is joined by Ivy, who takes advantage of the nearby greenhouse balcony to restrain him. Over the course of the struggle, Ivy's plants have released pheromones into the air that causes both Ivy and Harley to become aroused. Soon, they are all over each other, and their eyes turn to Batman. Batman begins as an unwilling participant, but will eventually give in. Harley and Ivy will compete for the male attention, while also trying to enjoy one another.http://lopezmichael.deviantart.com/art/Poison-Ivy-vs-Harley-Quinn-119316604
You don't need total knowledge of the characters to play them; I'm hardly a die-hard Batman fan and probably won't know the difference. If you are unfamiliar with the characters, minor research of their traits, appearance, and dialogue will probably be sufficient for me. You can add your own spin on their personality as well, I don't mind. I imagine all three characters would be dominant and competing with one another.
I need either one female willing to play both characters, or two separate females willing to play one each.
Beyond the first scene: I'd be down for playing further than the initial scene as well, exploring how the three character's future interactions might be altered because of this experience.