I caught my two female cousins doing this exact same dry humping act. They called it "ride the wild bull". We were all the same age, and it was a more naive time, clearly. I was scared but they told me to join in, and I didn't want them to tease me or try to get me into trouble. They both laughed at "that stiff thing poking my bum". I think they both came, or came close to it, grinding away, and I remember one of them, Sara, saying "are you tired out?" when I flopped down on top of her, spent. Shortly afterwards she said "have you wet yourself?". lol. As I say, a more naive time.