It was also on vacation that I first saw my sister having sex with a guy. She'd met him a few days earlier, and when I decided to follow them that day, I was hoping to see them make out, but instead, something completely different happened. Without even looking for a particularly secluded spot, they spread out a towel on the grass in broad daylight and fucked in the sun. It's hard to find the words to express what I felt... I definitely came twice while jerking off!