1. It's when your getting a lucious blow job from your hoe and she seems to be enjoying it so much, that she chomps down on your meat package and it hurts so fucking bads that you pull you third leg out of her jaws and whack the the bitch in the face. In some cases, you might pull out while ejaculating and smack her while your white juices blow over her face.
2. When a loud, ass, annoying bitch is talkin so much that you back-hand the bitch to the ground so she can shut hte fuck up.
Joe: Fuck man, my girl Tabatha was bitin on ma dick so i had to whack-a-bitch.
Bobby: Damn man you can't be havin girls bitin on yo dick, bro.
Bitch: *falls and make a loud thuds and remains on ground holding her cheeck... but quiet
Kid 2: OMG! thank you! that bitch was givin my a fucking mean-ass migrain!
Kid 1: yeah, well sometimes you gotta whack-a-bitch