1. Since the days of hippies, when drug addicts were given free rein, the long fingernail on the little finger was used to accurately dose the powder of cocaine that the owner of the nail wanted to sniff. For this purpose, a natural "shovel" was specially grown on which the powder was raked. Even the measure of weight was "nail". Then some adopted this fashion, not knowing about this nuance - simply imitating slightly stoned or sniffed personalities due to their dementia.
2. According to some reports, in medieval France, among the nobility, it was customary to grow nails on their little fingers. Since, according to court etiquette, before entering, one should delicately scratch the door, and not knock on it with a fist.
4. The tradition of growing a nail on the little finger was among the Freemasons in the 18-19th centuries, but it had no symbolic meaning, rather it was easier to recognize the brotherhood at the meeting. (Quote) V. Veresaev. By the way, A.S. also wore such a nail. Pushkin. And in general, many aristocrats of that time grew the nail on the little finger to quickly print letters when there was no special knife at hand (letters were sealed with sealing wax).
5. A long fingernail on the little finger is often used by card cheaters in their "work". When performing a fraudulent removal ("volta"), the nail is used to bookmark when dividing the cards.
6. Growing a julienne nail was popular in the late 19th and early 20th centuries among pickpockets. A long nail was covered with a transparent varnish for strength, sharpened and used instead of a knife, which cut pockets and bags. A sharpened coin or knife is evidence. And the nail with the nix just bit off and it is impossible to prove anything.
7. It is interesting that according to the criminal foundations in the middle of the last century, thieves in law grew a nail on their little finger to show that they would not work in principle and to emphasize their complete innocence to physical labor.
8. But computer scientists and electricians sometimes grow a nail on their little finger (or other finger) so that it replaces a screwdriver. And they twist and twist the screws, by the way I do it myself :).