I stopped by to see someone I had went out on a couple of dates with, but never had it go anywhere because of her hot and cold mood swings. Still, she was somewhat fun to be around when she was in a good mood, so I dropped by. It was just her and her younger, very annoying sister.

Just when I sit down, I overheard the younger sister say "What about him?". The other gave a stern look and shook her head no. I asked what's up and the older sister rolled her eyes and said "She's just turned 18 and wants to loose her virginity".

I joking say "come over here and we'll take care of it right now". She did. The whole time we're kissing the older sister is saying no, don't you dare, stop it, etc. Once the clothes started coming off she gave up, went to her room and slammed the door.

We finished and got dressed. Older sister storms out and says "it's my turn"! Then the younger starts protesting until the clothes start coming off.

Saw the younger one some time later. She knew I had wanted her older sister for a long time. She knew I thought she was annoying, but was grateful I had sex with her and pretend to be jealous so her sister would also.

To this day, the older one still thinks her younger sister "got out of line, so I had to knock her back into place".