Taking a plunge

Term used to reference, in vague manner, a sex act that would be better left to the imagination. Used in similar fashion as yada yada yada, or another sex act, the “Z.J.”

Person 1: “I went to Steve and Leslie’s house and accidentally walked in on them taking a plunge...”
Person 2: “what even is that?”
Person 1: “If you have to ask, you can’t afford it”