This occurs when a naked male stands and pelvic thrusts repeatedly (more often then not in front of the mirror or his girlfriend) sending his penis and genitals violently against his stomach and rebounding into his taint. Thus creating the noise "Flapa Dapa".
An Israeli phrase for a person who behaves as if he is "Mentaly Defective". The source for this word is taken from the Israeli army, and it's an abbreviation for "Initial Psychological Rating"