Everyone has a thing that turns them on, but finger nail biting is where many people would draw the line.
In this 1972 interview, one fingernail-boner guy reveals how he was extremely ashamed of and self-conscious about his fetish. Scientific American
For an otherwise normal, 23-year-old male patient described by the Wisconsin psychiatrist Austin McSweeny in 1972, the most arousing sexual fantasy was the image of an obese woman nibbling at her nails...
"He could [only] become sexually aroused and experience penile erection by seeing or fantasizing the fingernails of a woman as they were being bitten by her. Occasionally, the mere sight of a woman’s severely bitten fingernails would cause the patient to experience a spontaneous erection … When the patient experienced the proper fetish situation, he could masturbate to the point of ejaculation and experience gratification. This was his only means of expressing his sex drive."
The psychotherapist’s request for the man to picture heterosexual intercourse or a vagina in his mind’s eye was enough to make him vomit.
Here's hoping this doesn't become a thing, because if there's anything the world doesn't need is a bunch guys wanking off to porn stars biting down on their nails.