I still have to go with the whole sister thing when I was nineteen. I know posted it here at some other point, but to abbreviate the tale;
I was involved with a woman who had been unbeknownst to me fucking a good friend of mine. I found out, and we broke up. Well, I was a big party hosted by the very same friend. There was much drinking, and said girl was talking about getting back together and wanting me, blah blah. Her sister, who was eighteen had been making googly eyes at me. Well, I got her alone, we did naughty things, and I went down on her for a good time, got my face all freaking lubed up with her happy juices. And lips still drying with the sticky goodness, I found my ex and gave her a big french kiss, lots of tongue, and we did naughty things. And afterward, then I told he she should go ask her sister what she'd been up to earlier that evening...