One whose chin is "slapped" by another mans scrotum; usually a homosexual act.
The generally accepted gesture to identify a Chin Slap is to point out the subject in question, take your index finger and tap your chin. The tapping of the chin can be done gently or performed in rapid succesion to inform others of the level of Chin Slappiness that is emanating from the target subject. Incredibly high levels of Chin Slappiness can be represented by a full, palm slap to the chin area, resulting in a cocking back of the head.
What a Chin Slap.
He's such a Chin Slap that his Chin Slappiness resulted in the breaking of his jaw.