This is not my story, but a friend’s.
P was fairly successful with women in High School and had been dating G for a while. It was well after their first date that the Worst Date happened. They had already sleeping together at this point.
P was lucky because his divorced father had recently been away quite often, so he and G were able to sleep together in the comfort of his home. His father wouldn’t have actually cared one way or another, but it made for more privacy.
One particular week his father was out of town and they spent most of that time in bed. They had a long date near the end and this, like all other days that week, ended in bed. P woke to hear the front door of the house open. He left G in bed and went to welcome his dad back.
Imagine his surprise to see his father and G’s mother. Assuming she had caught wind of their relationship and was upset P was ready to be yelled at, but then he saw that they were holding hands.
“Meet your new mother!” his father shouted.
G’s mother held out her hand to showcase a small wedding ring.
It turns out P’s father had been secretly seeing G’s mother even longer than P and G had been dating. At the same time their parents had no idea they were dating. When he went out of town, P’s father was going to Vegas with G’s mother, and they were married early that week. For at least a week P had been sleeping with someone that was now his (step)sister.
It’s not clear whether the relationship ended right away, or if it just wore out later, but any time any P is introduced to new people(new people he does not want to date) we eventually ask, “Did you hear about the time P had sex with his sister?”
It’s possible this wasn’t P’s VWD when it happened, but I’d bet that no other date since has caused him more embarrassment, and therefore became retroactively his Very Worst Date.