The Friend Group

I have a close group of friends; all are couples except me. Among the group there are many crushes, spoken and unspoken. Several of us are bisexual. When we drink together, the conversation usually steers towards sex, and even possible sexual interactions between some of us. But the couples' relationships and our friendships are to be preserved and protected. We could never, any of us, cross that line... Or could we? Sometimes I wonder what it would take for an orgy to break out among us, all of us together, finally unleashing our desires. What kind of small, inciting incident could nudge us over that line?