My sister-in-law is very attractive, and also very sexy. I was staying overnight at her house and in the morning took a shower. I was standing in the bathroom naked when my sister-in-law walked in.
I was so turned on to have her catch me naked that I had an instant hard on. She stood there watching me, and I was thinking this was going to be a very erotic moment.
After I gained a full erection, she just patted it twice, smiled at me and said "down boy", and walked out.
After that, every time she sees me she just smiles at me as if to say, "I saw your penis and I think it is very amusing".
My penis is a very good size so I can't think why she thought it was so funny, and I'm very embarrassed.