This is a throwaway for obvious reasons
I (18)M had sex with my (22)F sister
My sister and I have always been close
So it was just before Christmas and we both never really got each other anything for Christmas but this year we decided that we would. But I had forgotten and so had she.
I was sitting in my room on my bed watching TV when she came into my room and she admitted that she had forgotten. Now as a joke I pretended to be annoyed but I quickly said that I was joking and admitted that I had forgotten too. She then said “can we watch a movie” and being the nice brother that I am said of course. Whilst we were watching the movie she put her head on my stomach which then gave me an erection. She noticed this and started mocking me for it to which I claimed that I couldn’t help it and she laughed.