A modern term meaning cool
, good, sick
, talented or the likewise.
The antonym would be screws
, which is generally an insult meaning uncool and often homosexual
Person 1: Have you played that new video game? It's so nails.
Person 2: Ya, but I'm not very good at it. Are you?
Person 1: Ya, I'm good at everything.
Person 2: You're so nails.