Can't believe it happened.
We went to a waterpark hotel. We got a room together, my wife and her sister and her husband. We were getting ready to go to the waterpark.
My sister-in-law was in the bathroom getting ready, changing into her bathing suit, when I needed to use the bathroom. So I waited until everyone was ready and I stayed to use the bathroom and joined them when I was done. My sister-in-law's bra and panties were hanging there. I couldn't help myself. I grabbed both and smelt both of them, goodness I was hard as a rock.
I jerked off so quick, I came like a freight train. Wish I could have kept her panties.