mule's finger
When a woman's sex organs prolapse, and form a long protrusion.

Not a large following as a sexual fetish; not heavily popularised.
"Ha. That woman's got a dong."

"No. It's something much worse. I've been told that: after a really good pounding... when it's all hanging out... If it gets cold real quick or you startle her...then... she gets hard. She calls it her mule's finger."

"Eww"