The condition in which the knees tan several shades darker than the rest of the leg. Affects mostly Caucasianrace, but is noticeable to some degree In all races.
Jack said Sarah you sure have a beautiful tan and Sarah said yeah, but check out my Nigger Knees.
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failure shower.