* The wild weekend. A somewhat public figure wants to be humiliated in public. He's halfway across the world where no one is going to recognize him and wants to get it all 'out of his system' while he can.
* The powerful aphrodisiac. Maybe it's a biological imperative or an intentional dosing or just an accident in a chem lab, but one round isn't going to be enough for A and, of course, B is more than happy to enjoy that little problem.
* The competition. Two friends or rivals or frenemies settle on a competition regarding who can go further with the NPC which can be fun, awful, and simply exhausting for the NPC who has to keep up with them both.