My friend has working man hands. This man repairs machines all day for a living and when the day is over his hands are, well, gross. Dirt and grime is stuck underneath the nails and cuticles. When he came over, I asked him if I could photograph his hands.
Afterwards, when we were looking at the photographs and he said that he didn't realize how dirty they were. I assured him that was the look I was going for in the photographs.
Real men sometimes have dirt underneath their fingernails and it is OK.