A Hard Worker / Tradesperson / Blue-Collar Worker: Dirt or grease ingrained beneath the fingernails is often seen as a badge of honest manual labor, typically associated with mechanics, construction workers, gardeners, farmers, or landscapers.
A Nail Biter (Onychophagia): The nails are severely short, uneven, and bitten down past the hyponychium (the quick), which is characteristic of chronic nail biting.
Mechanic’s Hands: A medical and colloquial term for rough, cracked, or dirty-looking hands resulting from frequent exposure to oils, harsh chemicals, or repetitive manual labor.