Performed before oral sex. It is usually a humorous though sometimes awkward/angry situation. When a man with an erect penis bends his member in a downward motion, only to release it as said girl is going down on him, having said penis hit said girl in her face.
dude1: "Yo dude2 Amanda was about to go down on me and I totally Twig snapped her in the cheek"
dude2: "NO WAY!"
dude1: "yeah man she freaked out after it was so funny."