An extremely obese person's knees that are exposed and create a likeness to a butt view from the layers of extra skin that dimple and come together while standing or walking or the posterior image created when an extremely obese person is standing still and wearing shorts or a skirt
Hey Man did you see the Butknees on that whale lady on the escalator as we went to baggage claim??
Yah, her knees were like a bad fat ass.......cover that up! That should be illegal.