In college I had a class with a very cute girl named Tracy. I had chatted her up, and once gave her a ride home after class. We’d never so much as kissed (although I was sure interested in making that happen).
One day, I was walking by the house and knocked on the door. Nobody answered. I heard a TV on, so I knocked louder. The door was ajar, so I nudged it open and called her name a few times.
Finally, I hear a female voice calling “Come in”. I followed the voice into a dark living room - the only light came from the TV. She was on the couch. I apparently had awakened her, and I apologized. She said it was OK, and invited me to sit at the end of the couch next to her feet. We made small talk, and I was pleasantly surprised at how comfortable she was putting her feet on my lap. (I was making progress!)
Suddenly, she got very quiet. I assumed she was too tired to talk, so I excused myself and said I’d see her later and left.
When I saw Tracy a few days later, I apologized for waking her. She seemed puzzled, so I recounted the incident.
She replied, “Oh, that was you!”
It turned out that Tracy had a sister who looked a lot like her, who was dating a guy of a similar build to mine.
So while I mistook a complete stranger for her sister whom I was a casual friend of, she mistook me (in her semi-awake state in the darkened living room) for her boyfriend. Until she realized I wasn’t her boyfriend! At which point she was too embarrassed to say anything, so she just quit talking to me.
Tracy said her sister was very relieved when I politely left.
When I later met the sister, she joked, “I don’t remember the face!”