A sexual term used when a man and a woman are having sex. If the man ejaculates inside the woman's vagina without protection, or permission, the women then slides two of her fingers into her own vagina (most likely the pointer and middle finger), dips her fingers into the freshly spewed semen, pulls her fingers out and flicks the sperm onto the man's face with a flicking, or slinging motion, if you will. This action is usually followed by the comment, "I told you to pull out asshole!" or "How does it feel to be a daddy now?"
That dick Fred came in me last night, so I gave him the "Two-Finger Slinger!"