Crusties is an informal term for the clear or yellow crust that forms around a healing body piercing. Even a healthy healing piercing will seep and "crusties" will form around it. This is simply lymphatic fluid, which comes out clear and dries to a yellowish color. It is nothing to worry about and is not usually indicative of any problem. Healed piercings may also seep slightly.
The best way to clean it off is to soak the piercing in warm water, softening the crusties which then come off easily. If you do not soften them and the jewelry rotates through the piercing, these crusties may scratch and irritate the inside of the piercing (the fistula), delaying healing and possibly opening a channel for infection to enter the fresh piercing.