I did my best friend's sister. She is a lesbian (technically)
one night we were coming back from a bar and I was sleeping over at his place. I didn't really know his sister that well. We had seen each other very briefly a few times but that's it. My friend and I sit down for a nightcap and she joins us. I knew she was a dyke so I didn't try anything but I noticed she was getting affectionate.
My friend goes to sleep (too shitfaced) and she invites me over to her room where, after an hour of negociation, I gave it to her pretty good.
My friend and I never spoke about this. I don't know if he knows