Well I've been guilty of the fingernail thing on many occasions over the years, but it's usually not something I'm aware of at the time. I tend to get carried away and survey the aftermath later.
I do try to stop it if I notice I'm doing it, and I haven't really had many complaints.
Abaya - my fingernails are also on the plain and short side but they can still draw blood. Skin is not very tough stuff.