The action of the large lips of black people who eat greasy food (such as fried chicken). This action, coupled with bad eating manners tends to make grease drops and crumbs of food "fly" off of the lips and spray all over other people during conversation that should not be taking place with a mouthful of fried chicken.
Otis- "Yo Jahn, gimme mo'of dat fine tasty chicken over yonder!"
Jahn- "I aint gettin you no' mo' damn chicken, fool! You sprayin me down wit yo' gravy smackin lips so much I looks like a glazed donut!!"
Gravy Smacker. A black person with large, gravy smackin lips. A black person known to eat greasy food (such as fried chicken) and talk with his mouth full, thus spraying grease droplets and crumbs all over other people within range.
Miriam- "Look at all these fucking gravy smackers! Let's go somewhere else to eat."
Webster- "Yeah, you're right. I should have known KFC would be full of gravy smackers. Let's bounce!"