HIMYM Alternate Ending #33: Menage a quatre
"Kids, this whole story of meeting your mother is my way of saying I’m sorry you had to see that today. We’ve kept it from you a long time, but you should know: your mother likes to do couple-swapping, and obviously Uncle Barney is up for that. That’s why we’ve had the hot tub all these years. It wasn’t just therapeutic. Well, it was in a way, but anyways…"