Do old people actually use "toe knifes"?

So I was telling my mom about all the weird shit they had Danny Devito do in Always Sunny and the "toe knife" scene came up. She told me that my grandpa used to do the same thing, not to cut his nails per se, but to take out any dirt under them. Thinking back I do recall seeing him do that too, no botched toes though.

Is this somewhat common or was my grandpa just a weirdo like Frank?