5. Dirt under nails
Personally, I find the whole concept of nails in the human body quite pointless. I mean, yes sure, we needed them as a form of claws to defend ourselves in the prehistoric times but in the modern era, they are pretty stupid. Instead, they provide a good place for dirt to accumulate under. The bigger your nails, the more the dirt stored. And its in our human habit to take a pointy object to dig out the dirt.