My legs are generally very hairy but the hair on my left knee is significantly thicker than the rest of my leg and my right knee. Not only is there more hair on the left knee, but its brittle and the skin under it doesn't look that healthy. It's bumpy, as if the pores are all raised.
What I believe caused it is when I was about 12 and had just started growing leg hair, I took a razor and messed around, shaving some of the hair off my knee out of curiosity.
I've tried waxing the area in hopes that it would grow back normal but it didn't.