The act of ejaculating in your hand and then slapping someone in the face with that hand.
Jason: "Dude what happened to your face?"
Kyle: "I called Justin Fat and that bastard gave me the money slap!"
Jason: "Damn i guess you wont be Talking shit about him no more"
When a fat girl won't stop talking about how fat she is so you slap her with any variety of oscar meyer sandwich meat. Preferable extra-long hotdogs, and then proceed to say "even fat girls can suck weiners!"
When Martha was complaining about being fat, Richard did the oscar meyer slap to get that hoe to shutup.
Open handed strike delivered to people of far inferior physical size or strength to show they are not worthy of the time it takes to bunch up a fist and hit hard when a simple slap will do.