refers to anything really gross and repulsive. Nadsty also refers to a used Nad (or similar hair removal product) that is covered in clumped up pubes or other hair.
I went to pick up this bitch for a date, and when I went to the john to piss before we left I saw a nadsty pile in the garbage can that looked like a dead chinchilla.
Anything that is as gross as a dudes nads.
From the root words nasty, and nads.
Gross man! that chick you were with is nadsty !