I dated a gymnast that could do a straight leg split on one foot. That is one foot on the ground and her toes on the other foot pointing to the ceiling, and hold it there for 30 seconds or so.
She could also sit on my face and and bend backwards and suck my dick, which wouldn't be nearly as impressive if I had 8 inches, but I'm not nearly that well blessed. She would have to press her nose to my stomach in order to accomplish this.
All of which is fun and interesting, but doesn't necessarily translate into the best sex.