Wicked sister and friend
When I was 17 me and my friend encourage my 15yo brother to get an erection and show us.
At the time I had never seen a real cock so when my friend came up with this idea I went along with it.
We told him we would give him money which we never did and my friend said she would show her tits to him if he gets it hard, he agreed and went out the room, when he returned he still had his pants on and my friend said no money if you don’t show us.
Eventually he did show us, it was thin and long and was pointing to the ceiling.
I can remember my friend burst out laughing and my brother run off.
Even when I was 15 I would have said, "Tits first!"