I was set up with #5 by the friend I had a threesome with #2 with. We were in a phase in college where strip poker was the norm at one of my parties. He was "dating" one of a set of twins, and we had seen them both naked at the same time, but it had never gone past him taking the one twin home with him. Apparently, the other twin had a crush on me, and for her 20th birthday, she decided that she wanted to lose her virginity...to me. We talked about it a lot at the beginning of the night, and I made it clear that I was not looking for a relationship with her, and she was OK with it...she just wanted to have sex.
I took it slow with her, knowing it was her first time, and although she had no problem with my girth, she had a hard time accommodating my length. The sex itself wasn't that great, and she had a lot to learn yet about oral, but I was able to get her off a couple times by going down on her before we did have sex.
This one will always be memorable, as it was set up by a friend that I had watched have sex in a threesome, and he set me up with the identical twin of the girl he was having sex with.