It is customary for Greeks to spit to ward off evil.  If a Greek hears bad news they may spit on themselves three times to ward of the possibility of anything bad happening to themselves. The person  does not actually spit on themselves what they say is "Ptew, Ptew, Ptew" with very little spit actually being thrown down onto their chest.  They may even raise their shirt and spit between their clothes towards their chest. 

Greek Fishermen may spit into their nets so that they will ward off any evil allowing them to get a good catch.

If someone compliments a Greek to avoid the Evil Eye they may spit onto themselves, and may say to the person "Ptew, Ptew mi me matiasis", which basically says, "I'm spitting on myself so that you do not cause the Evil Eye to come upon me."  Spitting is believed to be very effective against The Evil Eye.  Please check The Evil Eye.

Even in the Greek Orthodox church during the rite of Baptism the priest will spit.  When a child is baptized the priest will blow into the air three times to glorify the Trinity, and spit into the ground three times at the devil.  The three times spitting is believed to come from this.