A term used in the Marine Corps that occurs when someone is usually in a lot of trouble. Sometimes, the person isn't even in much of a shit sandwich, but gets harshly corrected for a small mistake, usually in front of many others. Simply put, punishing someone.
Hey Lieutenant Smith, did you see Lieutenant Schmuckatelli getting his pee-pee slapped by the Captain? Yeah, he is constantly smacking pee-pees.
I swear, if I see one more Marine wearing the uniform improperly, I'm gonna start smacking pee-pees.